Are you guys using the 2.6.11 version?I used to have a similar problem with GIMP, I think the version I have now is more stable -or maybe it's my PC having more RAM than the one I had the problem on -could be anything really...i use GiMP on Vista too.
sometimes though, it decides it doesn't like my PC and won't run properly, so i've got Irfan View as a back up.