You will need to configure the firewall to allow the Limewire program and you will probably need to add the ports/protocols needed by Limewire to function. Note, however, that Limewire and other file sharing networks are havens for malware, which is a good enough reason to not use it. If you are planning to use Limewire for legitimate, legal P2P file sharing, consider a safer alternative.
If you really must use Limewire and can't get it to work with the OneCare firewall, please contact support.
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve