6891 - 6900 (used for filetransfer), If you detect that are used other ports, it is that assurance that using alternative messengers as Gaim, Pidgin, amsn, etc. Microsoft respects these ports for the transference. .
take a look at this page http://support.microsoft.com/kb/927847
File Transfer TCP 443, 1863 TCP/UDP 1025 - 65535
jajaja 1025-65535 they are joking, aren't they???
i have transfer files via WLM to another WLM and I saw ports like TCP 4844
i think the best way is to use layer7 but the string suggested in the layer7 proyect site doesn't work for me
pd:gracias por el saludo rastafari