Is it safe to travel to Auschwitz from Prague via night train?

See www.seat61.com. Get a couchette and make sure it's locked at night and you'll be fine. Thefts (but nothing worse) sometimes happen to people falling asleep in the general seating carriages. Oswiecim is as safe as any normal town, the hotel is a 20mins walk. The museums open at 8. Taxis are not expensive, available 24/7, ask the hotel.
You're not taking any time to visit Krakow? Consider staying in Krakow after Auschwitz, then fly direct to Stuttgart with Germanwings from there for about €50-70 if you book now.

If you are in the seats take a lock and lock your belongings to the seat/overhead storage section. Thefts are the worse its going to get.
It seems a waste to go there and not visit Krakow. But each to their own.

Definitely get a couchette and lock the door to keep petty thieves at bay.

Oswiecim is a fully functional Polish town - no problem getting taxis at any time of day or night. When you're there in daytime, make a note of taxi numbers (all displayed on the taxis but usually without the notaitonla and local codes you'll need from a cellphone). This means you can call a taxi at night if there's none to hail on the street.

No particular dangers of walking alone, but late at night as in any other town you risk unwanted attention from people who've had a few too many in the bar. Not a god idea to wear a tiny skirt, low cut dress, high heels and fishnets, otherwise you'll be fine.

Your journey will be made all the more poignant by the fact that most of Prague's jewish population would have travelled on the same track during WW2 to meet their fate in Auschwitz.

Thank you guys so much for your replies, they are indeed very helpful:D I decided to visit Auschwitz because I have read quite a bit on the WWII history back in school days and I wanted to see history through my very own eyes. As I am planning for this trip I am pretty worried about traveling to Poland alone because I didnt have any friend who have been to Poland. But looking at some of the forums they commented that Poland is relatively safe now and the younger generation does speak english. I will be bringin my phrasebook, just in case.

And I guess you are right about Krakow, it will be a pity if I dont visit to Krakow since I am there. I have been looking up on the flights and yes I managed to find a budget flight from Krakow to Munich (which is my final distinction, I will just take a train to have a day trip at Stuttgart instead)

Unable to get a budget flight to Krakow, I will take a night train from Prague to Krakow (and yes I will be taking a couchette, a sleeper is way to expensive for me.)

I presume it will be easier to get a day trip from Krakow to Auschwitz. Any recommendation on a good guided tour?

#4 "yes I will be taking a couchette, a sleeper is way to expensive for me"

Er, a couchette is a sleeper.

Although you asked about Auschwitz specifically, now you say your worry is about Poland generally. You should not be worried any more than elsewhere in Europe. I went with my family to Poland for our summer holiday this year. I let my kids and wife wander around alone just as I would at home. Here's some pics:
http://www.flickr.com/photos/smithfamily1/sets/72157624737892676/
Not spectacular pictures, but you should note how normal everything is. Poland is a modern European nation, no need to expect special polish dangers lurking around every corner.

Poland is relatively safe now

No, it's safe, period. Probably much safer than from where you're from.

I'd also suggest that Salzburg is a more worthwhile daytrip from Munich than Stuttgart...

sorry but taking couchette will not make you safe. thiefs has their own keys - i know this from my own experience.

i am polish and i avoid night trains. Poland is safe, but trains arent

"Couchette" and "sleeper" can mean different things in different parts of the world. Generally, trains have two kinds of sleeping trains - those with 2-3 beds and a sink and better sheets, which are more often called "sleepers" and those with six bunks and cheap-nasty linen, which are more often called "couchettes." Couchettes are like hostels, sleepers are like hotels - the line blurs.

thiefs has their own keys

Couchette and sleeper compartments have their own extra chain or other lock on the inside too - use them.