The GIMP 1.2 should run on Windows 95/98/ME/NT4/2000/XP. It is recommended to use an NT-based version of Windows (NT4, 2000 or XP) for GIMP 2.0. The amount of memory can be an important factor, especially if you intend to work on large images. A minimum of 64 MB of RAM is recommended, but several GB do not hurt.
GIMP 2.0
GIMP 2.0