That's a problem with Apple's shoddy coding in iTunes, not with Windows. Winamp worked perfectly on my Pentium 100 mhz back in the Windows 95 days to listen to mp3s while working in other applications.
Not that you care, no one was even discussing Windows, you're just baiting for answers. I should just move you to my ignore list, like everyone should do.
I doubt Winamp existed when the Pentium 100Mhz was new or 5yrs old. However you may have installed it on that machine. Btw, Winamp doesn't have services running as a process like iTunes does and many AntiVirus software either by default or prompting users to disable those services. Some other apps may prompt to disable those during their installation. Did you give thought that his friend could've had a badly performing Windows machine or a pirated & hacked build of Windows? There are other variables that could affect application performance.