Fred,
Even with a fast processor, XP has so many things going on in the background that it produces glitches or "ticks" in the recording in spite of having all other visable programs turned off.
There is information available on the web. One is
www.pcmus.com/TweakXP.htm but if you Google for the subject you can find more.
I use a laptop for recording and I finally got mine cleaned up.
Also, there are free programs that allow you to save your individual setups of services and select them as required by name.
It's worth the effort.
Walt