I can;t listen to previews on MY PC version on the iTMS, it works fine on my Mac, but for some reason, even on the same network, the PC can't preview at all (I tried prebuffering it too, and it just sits there), while the Mac can?
Check your XP Firewall Settings and certain port-blocking apps. (Virus scanners etc...)
And check the Apple Knowledge Base for errors and workarounds 🙂