It sounds like one of them is firewalled. Most likely it will be the windows one. Do this test on both mac & pc LW to see which one is firewalled: Do this test aftr LW's been open for at least 20-30 mins or more: Bug Report instructions & sample image If it says True then it's not firewalled, if False it is.

Configuring firewalls to allow LW full access: http://www.limewire.com/english/content/firewalls.shtml Are there any other firewalls you have?

It might also be a router issue with port forwarding. Is one of them port forwarded?

(Did you know if you had iTunes on both comp's then you'd be able to play each one's playlists!)