Oh whoops. Ash, I missed the part where you said you used photoshop...
Gimp is not better than photoshop... Hehe
But I would recommend Irfanview. You can use it along with Photoshop or any other graphics program.
Irfanview is a free graphics editor program that makes working with screenshots a painfree experience. You can get it here:
http://www.irfanview.com/
It has one of the best BMP-to-JPG conversions; much better than even Photoshop. It'll even help to reduce the size (harddrive size) of your images. It's really good for making pictures so that you can post online. Just look at this:
No jpg distortion, no color banding, great quality
From a different game, but you get the idea...