I know this is a Mac forum, but there are certainly enough people with PC's laying around that you could attempt and confirm this bug.
Windows XP sp1 with two NICS installed. One NIC is connected to a DSL Modem and the second NIC connected to a switch that also connects my Mac and second Windows box. Internet Sharing is turned on the first PC.
If I launch iTunes on the Primary PC, all internet sharing stops. Close iTunes and internet sharing starts working again.
I have already sent this to Apple, but I figured we could at least confirm the bug for them if anyone is interested in testing it out.
Regardless, it just means one computer that I will run WMP on, but everything else is iTunes all the way.
Later,
dw9