Well I use photoshop on a daily basis so can help you there. PS 6.5 and 7 have a "save for web" utility that is terrific for exporting images. Much better than just using the "save as" function.

Upon export you should see a page like the one attached. Although my sample image is black and white, it's an 800 x 600 image originally at 1.4mb and upon compression to JPG, with no image quality lost, ends up just over 100k.

If you have an older version of PS, the "save as" function and 60% of image quality will work just fine. At 100% you're seeing no appreciable compression and no file size savings.

EDIT: and I used a PNG here since I was mixing photographic and program screen elements. PNG is a good format, but a little orphaned I'm afraid.