Im guessing you bought vista to install on that machine? If so, extremely bad decision. That cpu is very outdated, and you have an extremely small amount of ram for vista. If you have the cash, you'd be doing yourself a favor getting a new system.
that could honestly be a possibility, it could be very likely that all your ram is filling up and some of your cached files such as your audio files could be pushed back into paging files on your hard drive, which would quickly explain why your audio is slow,
was the sound all distorted, before you switched to vista? you may also want to stop all background applications, then attempt to pay whatever if it runs clearly then you may need to get another stick of ram, or downgrade back to whatever was on the computer before hand