This should answer your questions & then some: Budget travel basics for Southeast Asia - the important links are noodle pie (it will blow your mind on food - see menu to right - pick your food, oh man), Travelfish, Man in Seat 61 (trains), and check out some of the travel blog links.
Definitely get a guidebook - I like LP, though there is no perfect guide. As Tim says, Get a guidebook and get lost!
CK

Hmm, there is really nothing I haven't eaten, including shellfish, and I live to tell the tale. Have had a few bouts of the runs, but nothing serious. The two precautions I take are a) washing my hands frequently b) popping a de-worming tablet every 6 months. Oh, and I have my Hepatitis vaccinations.
Wow, thanks so much! That's a lot of great information. I'll study it and probably have more specific questions, but thanks to all of you very much, this is more than I'd hoped for!
Chris

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<hr>Otherwise I eat just about anything, even ice - which guidebooks constantly say to avoid, but which has never, never given me any problem in Vietnam ...<hr></blockquote>
Personally, I think this thing about not eating ice is the biggest single fallacious health myth I've ever heard about travelling in Asia. Ice practically ALWAYS comes from factories that produce it under sterile conditions ... Admittedly, people do leave it lying around on footpaths and stuff, but that's also true of the meat, fruit and vegetable you eat ... the water that is used to make it is almost ALWAYS good ... It's trully the mark of a rookie to refuse the ice in pineapple juice .... which might well have been watered down with tepid tap water .... seriously, ice is the least of one's problems ...
Agree that shellfish are worth avoiding except at absolutely top-range restaurants ... and that doesn't include buffets at five-star hotels ...
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<hr>except at absolutely top-range restaurants<hr></blockquote>
I agree with most of your point, but not this one. The only time in my life I had a really bad case of seafood poisoning, it was after eating in a very posh restaurant (not in Vietnam).
Seafood, and indeed any produce, can be contaminated even in the cleanest kitchens, all it needs is for the cooling chain to be broken somewhere, or the food to be cross-contaminated.
However, above is true regardless of where you live and what establishments you frequent and thus there is not much you can do (short of eating and drinking all together, of course:-))).

Hanno,
Yeah, Tony Bourdain did a whole chapter on the subject: "Never Order Seafood in a Restaurant on Monday". Bit of an eye opener. Agree with you that the cooling chain can break down at any level - but it's almost a sure thing when the mussels are sitting in a bucket by the side of the road. I'll eat fresh oysters at good restaurants - but if it's crayfish, I wanna see it alive and kicking beforehand - I know that a LOT of Indonesian restaurants use crayfish that have already died of causes unknown ... which can kill YOU if you are unlucky ... or at least give you a pretty horrible week ... Tony Bourdain makes the good, if obvious, point that you should always order quick moving dishes, or eat at restaurants with a high turnover, for the best chance of fresh food. You shouldn't order obscure dishes, because the ingredients have probably been at the back of a frequently opened and closed cooler for months ... power outages are an added bonus in the developing world ... If you ever get one of those 76-page menus, ignore it and ask the waiter what's good and available ... they probably only really do four dishes really well ... The special of the day is usually a good bet, unless it's an obvious attempt to get rid of leftovers ... As you say, these are universal eating rules, they don't just apply in Vietnam ...

Don't have a link to that Tony Bourdain article do you Jakartaboy? Sounds like an interesting read!

Gingbuoy, it's a chapter in his book, "Kitchen Confidential": it is an excellent read! Here's a teaser:
"Monday? It's merchandizing night, when whatever is left over from the weekend is used up, and hopefully sold for money.... Chances are good that that tuna you're thinking of ordering on Monday night has been kicking around in the restaurant's reach-ins, already cut and held with mese-en-place on line, commingling with the chicken and salmon and the lamb chops for four days, the reach-in doors swinging open every few seconds as the line cooks plunge their fists in, blindly feeling around for what they need. These are not optimum refrigeration conditions ..."

We never ate any raw shellfish, but didn't think twice about eating the excellent shrimp, squid, and crabs in Vietnam---in restaurants that seemed busy where others were eating these things. Never got sick, but maybe we were just lucky? It all seemed as fresh or more so than the shellfish here in Boston. But we did stay away from juice that might have been made from tap water, and ice. At first we tried to avoid uncooked vegetables, but the herbs and greens are so much a part of Vietnamese food that we eventually started eating them. But never lettuce. We didn't eat street food, but really the line between simple restaurants and street food is probably quite fuzzy. My experience in any country is that if you are going to have digestive trouble it will usually happen about 9 days after arriving in the country. Don't know why this is.
But the food was a highlight of Vietnam.
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<hr>"Monday? It's merchandizing night, when whatever is left over from the weekend is used up, and hopefully sold for money.... Chances are good that that tuna you're thinking of ordering on Monday night has been kicking around in the restaurant's reach-ins, already cut and held with mese-en-place on line, commingling with the chicken and salmon and the lamb chops for four days, the reach-in doors swinging open every few seconds as the line cooks plunge their fists in, blindly feeling around for what they need. These are not optimum refrigeration conditions ..."<hr></blockquote>
What and where he talking about?
Weekend is, still and will be the busiest time in the restaurant business. is this book talking about in some Muslim countries that closed all things down in the weekend, it's not possible happen in other country.
There are few refrigerators in the kitchen, one walk in for flesh veges and also use for defrost and few under the counter for the line cook and those cooling trays on top of those counters. Meats and seafood are separated by kinds, so the cook knows exactly where they are located. This is in one of the dirtiest restaurant (a Chinese restaurant) do.
You guy are talking things to avoild, if I wanted to avoild anything (witch I do not) it would be vegietables because the use of chemicals in here are have no control what so ever.