Also, glynor, can you explain more about this... ... like, how do you do that and why is it limited?
Sorry... I missed this question.
Mounting a network share is simple. First off, make sure you've shared the directory on your Windows box. I won't really get into this, but if you have Windows XP Pro it's quite easy (it's possible but limited with XP Home). Google "share windows network" or something similar for more info. I've also previously posted tips on this process here (in response to KingSparta not too long ago I think).
Anyway, once it's shared properly, on your Mac simply go to
Go --> Connect to Server (from the Finder). You can either browse the network for the share or type in your server's IP address. If your router can handle internal DNS or static hosts you may be able to enter the machine's hostname instead. After you connect to the remote machine, it will ask for a username and password (enter the one for the Windows machine, not the OSX box) and then present you with a list of the shares on the network machine to connect to. You can save the username and password to your keychain and it won't ask for them again (unless it changes).
Once you do all of this, it will "mount" the remote drive on your desktop just like you'd inserted a CD or connected an external drive. You can then add the files to iTunes and do whatever else you want with them.
There are actually quite a few limitations of this system, but the biggest is that you have to have an account on the "sharing" machine and be able to directly connect to it!