I bought it in early 07, I think. I don't believe it's a 64bit computer and don't know how to check. I just thought it was weird that the system was only recognizing one and a half sticks of RAM.
Click the Start Menu, then move your mouse over to where it says "Computer" and /left/ click. Now select "Properties." This will show you your processor and operating system type.
If its a 64bit computer, when you upgrade to Windows 7, make sure you get the 64 bit version.
If your just using the computer for the 'net, it's probably not worth the extra scratch. If you use Photoshop, rendering packages, CAD, and so forth then it is.