Actually, just grabbed WMC 2.0 earlier (didn't even know it was out), and tried it on the notebook. I told it to share \\central\media\music (my music folder), and after it scanned, the XBox 360 saw the music and could play it back.

My Samba implementation might be a bit different though, as I have mine set up as an NT4 domain that my notebook is joined to. Though maybe my samba settings for the share will help:

[media]
path = /home/media/
write list = drakino, user2, user3, user4
force user = user5
force group = users
create mask = 0774
directory mask = 0775
guest ok = Yes

I do the force user and permissions to avoid any issues with user 2 unable to delete something user3 put there.