The standard screen size when I started (a fair while ago) was 640 x 480. Nowadays, most people tend to use at least 800 x 600 or higher BUT there are also an increasing number of phone / PDA type devices with smaller screens (eg. 320 x 240 or less) or different aspect ratios (eg. more 'portrait' than 'landscape').
Therefore, you've got to think about who your audience is. My rule of thumb is that less clearly I can define my potential audience, the more flexible I have to make the layout, and that sometimes means sacrificing some of the really 'cool' things I could do in order to give everyone a useable site.
For example, if you look at my band website (see my sig, below), it will work on a wide range of screen resolutions. It could be flashier, but then I'd have to start making more assumptions about my visitors.
On that site, I've also incorporate a 'blog' from Link Removed to make it easy for me to keep the news up to date - something like that might be a helpful idea, as having a nice looking site that is obviously out of date is almost worse than having no site at all!
Wulf