Can't use 2.5?

I just downloaded 2.5 onto a flash drive and took it home last night and installed it on my pc. I’ve done this with 2 previous versions with no problem. When I tried to run it, it brought up a blank Blender screen and a message popped up saying something like unknown file or file source, or something like that. It then proceeded to load 2.47 which I still have on my pc. Has anybody else had this problem? What’s the difference between the 32 bit and 64 bit versions. Maybe I downloaded the wrong one? I think I got the 32 bit. I don’t remember.

Also, even though I’ve had Blender for some time I’m very inexperienced with it and animation in general. Haven’t been able to do much. I was wondering if anybody knows when any tutorials might come out for 2.5 for people with virtually no experience. I would like to get into this learn and create my own projects, especially for my nieces.