LOL
I don't think Suzy83 expected such verbose explanation...
anyway, nice to see some ppl here who know well the network mechanism thingy. (svmedia, wivern, thx)
Indeed, duplicate Mac addresses are not necessarily troubleshooting. We can extrapolate this to duplicate IP addresses...if the duplicates are sufficient distant from eachother, one might not experience problems directly.
For tracking down this kind of protocol problems, this is why some ISPs want to have your NIC Mac address.
Nederfox
EDIT: @svMedia:
When connected to the Msn network, a constant connection is opened to baym-cs174.msgr.hotmail.com:1863.
This machine could act as "man in the middle".