hi!

Yes, lots of people tour Vietnam. Hanoi to Saigon or v v is very popular.

Firstly, I suggest you go N>S at that time of year due to the wind.

Also start your trip a bit further north - the DMZ may (or may not) interest you, but Hue is well worth a visit. This will be more interesting than the last bit into Saigon.

You could also think about going via Dalaat.

Excellent suggestions, also keep in mind that the coastal highway is quite busy with traffic but pretty well flat as a pancake. The road is great but it's not quiet... If you go into the interior, it's a very different experience, far less busy, more hilly and roads are sometimes in a bit of disrepair. Unfortunately, the weather in the north isn't the best in February...a little rainy and cold. Personally, Hue was my favorite town on the coast.

How easy is it to do this independently? (i.e without tour guides/companies)
I'm hoping to arrive in Saigon/South Vietnamin about mid-may june time, and was wondering how easy it was to pick up a cheap bicycle and a few spare inner tubes before I set off, and then see how far I can get before it breaks down haha

To answer #3. It is easy to cycle in Vietnam independently. Accommodation is easy to find and towns not too far apart along Highway 1. Motels are being built along the more remote stretches of the new Ho Chi Minh Highway through the highlands (National Routes 14 and 15).

Avoid riding at night because: 1 - highway robbery is real in Vietnam; 2 - the roads can be so bad you need to see them in daylight; 3 - VN drivers are maniacs and you are likely to be forced off the road and killed at night.

May-June is summer and the winds you will have tail winds going north. For those heading south, do this in winter to have tailwinds.

Hanno recommended this bike shop in Saigon:

Golden Rose
Shop 51/1 Sky Garden 2, Phuong Tan Phuong,Phu My Hung
District 7 Saigon

For spare parts:
Mr Tri, 285 Vo Van Tan. (Ward and District not known)
You have to ring the bell to go in and he has a workshop inside with a massive supply of components

A heavy clunker of a trail bike starts at 2million DVN in Nha Trang, but you are likely to get a much better bike in Saigon.

Buy the best VN road atlas in Saigon so you can see where you can to get off Highway 1 as much as possible. The atlas is:

Tap Ban Do Giao Thong Duong Bo Viet Nam, Nha Xuat Ban Ban Do (Cartographic Publishing House), Hanoi

It does not show roads buiilt in the last four years, including the new Nha Trang-Dalat road, and the scenic coast road from Cam Ranh to Nha Trang.

I am also biking Saigon to Hanoi in March but want a tour company.
Did you hear of either:
1. Vietnam bike tours // Van phu Thuan co Ltd
2. Bike tours Vietnam - Asia Pacific Travel
They both book your hotels, supply bikes, guide and take care of your luggages.

Does anyone know whichone of the 2 companies does a better job?

I enjoyed a ride the length of Vietnam in Feb.-April of 2009, and can recommend the route that I took. I rode northbound and didn't find the winds too much of a problem at this time of year; some days I got headwinds, some days tailwinds; if you have the choice, riding southbound will increase your chances of tailwinds. Besides a travelogue of the trip at www.crazyguyonabike.com/doc/AsiaAgain</a>, there's a "Route Details--Daily Stats and Notes for Cyclists" section with practicalities such as places to stay and road conditions.

There's no need to take a tour, going independently give so much more freedom.

--Bill