css files not updating in localhost (XAMPP test server)

I've got an issue with a web page I'm developing where the .css files that I attach to the pages will not update on my local host.  I can make a copy of the file with a different name and link it to the page.  However, if I name any file a name that I've already used then the CSS reverts to whatever was on the original documents.  This is making my php page testing a pain when I view the page in a browser.  The problem doesn't seem to occur for my other websites, and completely goes away when I select "none" in the testing server options.  I'm using XAMPP to run my localhost testing server.  I'm using Dreamweaver CS4 on a Vista machine.  Any ideas?  If nothing else it would be nice to know how to delete the old files that are stuck in the testing server directory.