Hi Everyone,
I have feeling a lot of you probably already know about this WinXP trick but it was new to me so hopefully it will help someone else.
1. Launch a mame game
2. Press Control-Alt-Delete.
3. Right click the mame process (not the frontend) .
4. Click "Set Priority".
5. Set the priority level to High or Realtime.
6. Close Take Manager.
This has cured almost all of my performance problems, especially sound. Although, it is a pain doing this every time I run a game!