To Answer the first portion of you post, Yes you can run a 32bit OS on a 64bit chip, they are backwards compatible. And your right, the 64bit market is small. they primarily made them for large businesses that needed more computing power, although, they are available to end users. I have an AMD 64 3800+ I have ran both 32 and 64 bit OS'es including windows and Linux. At this moment in time, 64 bit isnt changing the computing revolution mainly because there are so many people that still have a 32bit processor, and when the 64bit cpu's came out they were rather expensive. if you decide to go with a 64 bit OS you can still run 32bit apps with it. as for the differences of 32 bit and 64 bit, I cant really tell you, other than it can handle more instructions at one time. therefore making it more reliable and easier to work with, maybe someone else in here with more knowledge about this can answer that question. Right now I'm running Windows XP Pro 32bit on my 64 bit CPU. I would recommend staying away from XP Pro x64 because its kinda bloated and it will actually run slower on your maching rather than faster, I thought this when I installed it and it in fact ran slower, thats when one of my good computer techie buddies told me that the x64 version of windows is bloated, so I went back to 32 bit. I hope I have answered all your ?'s and if you have any more just ask me, I'll try to answer them accordingly.