Hmmm, I go to "File" "Save for the Web" and then size it to 600x600 pixels and adjust the slider bar of quality until the image is 150 KB or less. Does that help? It might be a tidge different in PSE 5.0 ... but maybe this will help.
Edited to Add: I resize my image to 8 inches by 8 inches before doing Save for the Web ... otherwise it gives me a warning that it might cause issues with my 'puter.
Good luck & Hugs!