usually you want to use the resolution of you monitor, screen, ting that shows stuff, whatever you call it. i usually make mine 1024x768, like KoRuPT.
Make it 1600x1200 because if you needed to make it smaller for another resoultion, it will turn out good.
^you could have edited your post... anyway, If you are just making it for yourself, make it the revolution that your screen is at.