Win2000 versus Win server 20003 on old hardware

I have an older box, AMD Sempron 2400+, 1GB ram, that I use for to run a
couple of half-life servers. I upgraded it from Win2000 to server 2003, and
when I did I noticed a significant increase in cpu consumption. On the
Win2000 box, the server executables would use maybe 30% cpu when fully
populated. On the Winserver 2003 box, it used 80-90% cpu. My first guess was
that the cpu scheduler in server 2003 has more overhead and the context
switches were using up all the extra cpu. My second guess was that I really
didn't have a clue why. On both installations I stopped all services I
didn't think needed to be running.

Anyone have experience running server 2003 on older hardware re.
performance?