Your biggest problem, honestly, is that your girlfriend is running WinME. It is the sorriest excuse for an operating system in modern history. But enough about me, here's some advice.
When attempting to connect a PC to a Mac to share files and printers, you have to tell both ends what they're dealing with. The PC really doesn't care what platform hosts the printer, since it will most likely dump a "raw" format job through the host anyway. However, the Mac (OS 10.2?) is kind of picky about what it associates with. I'm not 100% on OS X and more recent updates, but there's a SMB command you can give it to tell it to share with the PC-I just can't recall what it is.
Have you scanned the last 90 days or so of this forum for anything about print sharing? It's worth a look.