There is a Windows power tools utility that will change resolution as well as anything around, but only gives you three size options. It is worth a try though. It is a really handy routine to have on your computer anyway.
I agree with GIMP most likely being the best choice. It is easily as powerful as photoshop, and it's free!! It is also harder to use however...
How are you getting the screen shots? any way to reduce resolution on the front end??
