definitely use Cygwin. Its by far the best out there. Its free.. The intstaller/updater program it uses is awesome and compiled stuff is posted to the installer site very often. You can even run X-Servers and fullblown unix desktops on it.
Let's not forget the ultimate UNIX emulation for PC's: Linux. [img]images/icons/wink.gif[/img] (It's probably overkill if you just want to refresh your memory on basic commands and such, but if you really want to get into the meat of things....)