Hmm... don't know if you still care 'bout this thread, but I got some info it might be useful to you:
http://unxutils.sourceforge.net/That is a compilation of GNU utilities, as native Win32 executables. Don't know if it works for you, though... (Didn't found specific instructions of how to compile unrar using Cygwin, heh, I haven't tried, but I'm gonna give a try to it someday to see if I'm sucessful)