I am trying to install Gimp 2.8.0 on Windows XP. I get an error message "This version of Gimp requires Windows XP with Service Pack 2, or a newer version of Windows." But when I check my Windows version with Help -> About Windows, it says I have Windows XP Professional Service Pack 2. Any ideas what's wrong?
The error message is incorrect. Gimp 2.8.0 requires XP service pack 3 or later. This bug was fixed in later builds (by correctly saying that SP3 was required). You can see the link with the correct requirements on the GIMP download page.