Taken from The Gimp page...
GIMP 2.8.x should run on Microsoft Windows XP SP3, Vista and 7. Older GIMP versions (2.6.x, 2.4.x, 2.2.x, 2.0.x) could also work with older versions of Microsoft Windows, but they are not supported anymore. The amount of memory can be an important factor, especially if you intend to work on large images. A minimum of 128 MB of RAM is recommended, but the more RAM the better.
I Live In My Own World, But It's OK.....They Know Me There.