A three year old machines starts accumulated "stuff" that drags down the resources. Music players use a fair amount of resources anyway and when something else starts up, it's fairly normal to hear a slight jump..If your installed RAM is 256 MB or lower, you probably should add more. That would help. Follow the procedures in the links below and see if it gives the machine a little boost...
Ignore the first few sentences of the link below because WinXP doesn't display resources as listed, but follow the other procedures, especially check the "Services" links toward the bottom of the page.
How To Shut Down Unnecessary Start Up Programs
How To Clean Unwanted Files From The Hard Drive
Have you checked for spyware and adware? Use the three programs at the links below to do that. Download, install, update, then run the free programs that are provided.
I have a dell 8100 demension 3 years old and I am using windows XP. Whenever I start a new program and iTunes is running, iTunes would pause or skip for a couples of seconds. I'm using the latest version (4.7) When I purchased my iPod last year, I didn't have this problem. What is causing iTunes to pause/skip when a new program is opened?