you need the actual namecoind program also. go here:
http://dot-bit.org/InstallAndConfigureNamecoinit has directions and a link to the namecoin main page to download the windows namecoind program. point the GUI program at it once its installed and configured. the directions are bit sparse and it has linux and windows directions.
sorry I cant be more specific, I use ubuntu 11.04 for my namecoin stuff and just use the command line client (namecoind) directly.