http://www.teamstream.com/download.htm

It is ad supported, though, and according to my firewall, it actually modifies your Windows EXPLORER.EXE file which I DON'T like. (probably to display the ads)

However, anybody looking for a way to map an FTP or WWW server to a drive letter, this is for you.

There are others available but this is the only one I've found so far that is "freeware"