Don't something like 30% of internet users still use 800*600 though? seems like a large proportion to be missing out when it's so easy to cater for them.

Although in the end i guess it depends on what your target audiance is. If it's something for 'computer literate' people (which in your case it is) then i doubt many, if any, will be using 800*600. If it was something more general, however, i think it would be a bad choice to make.