the noise issue you will have to track that down.
avast is a light weight AV but it wouldn't harm to temporarily stop services not being used like email scanner and web scanner during games anyway.
Coincidently i have a gigabyte mobo with ide and sata,
when you setup the bios there is an option to run in 'ide' mode on yours its called 'combined' (from your manual) which puts the sata drives into pata mode now i have run my pc with a sata drive and a wd 80 gig ide drive, the 80gig was the original,
i noticed quite a a slow down, so i disconnected the ide and run the pc in full sata mode.
its a lot faster (for games), now this is probably because the old drive has a different sustained data transfer rate than the newer drive. So where have you installed xp ? on the 80gig?. if so move to the sata, drive if possible.
Also check where the page file is, i fiddled around for a while partitioned the sata into two made sure the pagefile isnt fragmented,
& basically i run the new drive only. The 80gig is usefull only as a backup, well mines a desk paperweight.
Additionally update your graphic drivers , nvidia seem to launch a new one every month lately.
And finally ive recently discovered ultimated defrag from distrix its on file hippo.com, now all i can say is its 'seems' to work ie optimize better than the built in defrag its worth a shot on standard settings.