Hi Peter,

Still be careful with windows 64 bit and make sure all your hardware can connect to it, ie driver support. Windows 64 has a different design and most people install it to address more memory, because 32-bit can address max 3,5 GB. Indeed what mark says, windows 64-bit is the future, but not every computer can run 64-bit since you need a 64-bit capable processor as well.

Indeed what Mark says, maybe something else is causing your memory loss.
Did you do all windows updates? Maybe a broken memory chip.
Do you run other programs together with your FS? Internet explorer/Firefox/Music program?

I myself run windows 7 32-bit and never had any problems so far.  

Did some quick google: windows 7 ran out of memory

http://www.sevenforums.com/gaming/2499-out-memory-error.html
http://hardforum.com/showthread.php?t=1433143

Hope it helps.

Edwin