machan, it should be 64 bit. you can get more information using the CPUZ software.
if you are going to have more than 3GB RAM, you have to use a 64 bit OS. Almost all sotwares available for windows can be installed on 64bit under compatible mode.
I have used vista xp and windows 7 64bit OS and they work great!
http://www.start64.com/
that site is dedicated for 64 bit OS.
One thing you could worry about is the driver availability... so if you want to go for 64bit, first i suggest you to go to manufacture websites and check whether drivers are available for 64bit architecture.. companies like ATI, Nvidia, Intel are providing 64bit drivers..
good luck...