My computer seems very slow at transferring files, and it
has problems playing back music as it stutters. It is a
AMD700 with winxp and 512meg ram. DMA is enabled, but CPU
usage seems to be 100% on even simple things.
Any advice?

I don't know about your sound. You might want to check how
many processes are running. If there are a lot, use the
System Configuration Utility to disable some of these
programs. But make sure the programs that you disable
aren't very important. Who knows? Maybe doing that might
also help with your sound problem. And about the CPU
percentage, I've usually found that to be wrong. I don't
know why, though.