Computer Issues

I am now getting a little pop up in the lower corner of my screen that tells be that I might have a "counterfeit" verson of Windows XP. Click here to resolve? Is this another shake down from Bill Gate and company? I always start having problems when I try to intstall Yahoo Messenger. I have install and uninstalled that blasted piece of software at least a dozen times over the last couple of years and everytime, EVERYTIME, it sucks up all of my virtual memory and all of the resources. My CPU runs at 100% and I get the "Virtual Memory too Low" message. My kids both run YM and I find it an easy way to say hello or help them with homework, but unless I can find a simple solution, it ain't ever going back on my machine.