what speed is the cpu? I think you're describing  one in the 2.0-24ghz range, not so?

If I were going new I'd go at least 2.8 ghz and 2g memory - not for Bryce so much (as I'm backing down to a 900mhz for Bryce to free up the main computer) but there is more to compter usage than Bryce as heretetical as that might seem - Thomas Covenant and TheBryster seem to be poping into my mind for some reason.

A couple years from now you'll be glad you didn't skimp.

FYI: the tests I've done on hal2 :hal1 (1.6g:0.9g)indicate that there is a direct 1:1 relationship between raw cpu speed and  Bryce rendering speed. Of course for you that's not conclusive and I imagine the faster your computer is the less reliable my observations will be. They're using all types of 'tricks' to improve clock speeds now days.   

Also I'd hold onto the old computer or give it to a friend - it just might need some TLC.

-TJ