What size should I..

What size should I make my pictures so that I get good quality and still not take up too much space on my .MAC account. My pictures import at huge resolutions so I have to bring them down a lot. I just dont know a good size for them so that I dont lose quality. Also Apple devs should add that feature in Iphoto when sending a slideshow to the .mac account. I thought it would have an option like that but I didnt see one. Somethign that prepares it for .mac site I guess. I dunno, any help would be appreciated and as always TIA.

1024x768

Pretty common size, but still small.

My favorite

If you're talking about photographs, I'd say make the longest side 600 pixels, Photoshop will decide how long the shorter side should be to be in proportion.