Cheers, but that wouldn't work for what I'm doing

basically let's say there's 100 customers, each uses a different stylesheet, we incorporate the page into their site so what I need to do is read the URL for determine the stylesheet, probably didn't explain it very well, still hungover. Let's say the URL is
www.wherever.com/index.php?css=customer1
I want it to then incorporate "customer1.css" (which'll be uploaded manually).