Currently Being ModeratedJul 9, 2013 5:31 AM (in response to mchangstein)
OS X is passing the Internet connection to the guest OS, it doesn't work the other way around.
You will have to install Windows into Bootcamp and I don't think XP is supported any longer, however Win 7 Pro+ will run most XP programs.
You'll of course be booting the Mac directly into Windows and thus OS X won't be running, thus you can't share the Internet connection to OS X.
Another alternative is to use a Windows 7 Pro+ machine to connect to the network and then sharing it's Internet connection to the Mac via Ethernet cable or wirelessly.