Hey Becki
I run my screen resolution pretty much as high as the monitor will allow (and still be readable).
But, programmers, webmasters etc usually run a higher resolution than the every day surfer (because as you will find out as friends ask you for tech support, many surfers don't even know they can change screen res)
My wife runs her at 800x600 but that is mainly because of a vision issue, she likes big text and all.
I design for 800X600 because I know that will work for most folks out there whether they are running a higher res than that or not.
I usually design inside a table at either 650 or max of 700 wide. However, there are times I will just use percentages, depends on what I am making