I am trying to re install McAfee but can't get past the screen that reports the alleged existence of Webroot Spy Sweeper w/ AntiVirus on my machine. Apparently this program conflicts with VirusScan, but I can't find anything Webroot-related via Control Panel, search or Windows Explorer... How can I delete it if I can't find it?

I won't ask your reasoning behind installing McAfee (as crazy as that is) however, there is a removal tool that you can download here

Have fun