Web page design help


I am writing for an online music magazine but the graphic designer has quit and have said that for my pages I can design my own layout. The pages will be jpeg format and 500x500 pixels.

So what I would like to know is should it be RGB and 72dpi?

I hope someone can help!
It's a free grunge one I found called Base02. I tried Trashed and Sidewalk but they weren't too clear when small.