As Mark said, there are a number of netbooks around now.
Most of them now have the 1024x600 size, but there are also some of the "older" netbooks that have lower resolution then that still. Mine for example has *wince* 800x480.
If you want to be really compatible, go for 800, but otherwise, I'd say your good with 1024, and as for the height, the user can always scroll.
