This is how I would do it:
Go onto your Mac and go to Sys Prefs -> Sharing -> Windows Sharing -> enable it, and your account.
then, on the PC, go to run: and your.macs.ip.address (123.123.1.123)/yourusername
i think that's what you'd do.
not sure if that's the right way for the run part, but maybe *goes and checks*
EDIT:
i just tried to do it on my pc, and it's just... sorta difficult, almost, well, not nearly as easy as on OS X. what you probably need to do is just connect to it through Finder -> Go -> connect to server -> Pc's IP.
then put your iTunes library in your shared folder or whatever.