Vista - Xbox 360 and Vista MC networking wired/wireless

I've been having trouble with streaming music and pictures from my Vista Home
Premium laptop to my X360 over my wireless network. I've called MS many times
on this problem with no luck. The situation is as follows: The X360 is
connected via an ethernet cable to my Netgear wireless gateway, which is
responsible for the network in the apartment. My PC uses this wireless
network to access the internet. I want to stream music from my PC to the Xbox
over the network.

The Xbox does not show up as part of my network when I check for it on my
computer. However, if I also connect my computer to the gateway via an
ethernet cable, I can connect and stream music as I desire. I want to be able
to leave my computer in one room and still do this.

I've messed around with all the firewall settings on my PC (even turned it
off) and have enabled port forwarding on the gateway for those ports that the
Xbox and MS websites tell me to.

Is there any way to set this up without either connecting my PC via ethernet
cable or buying the wireless adapter for my X360?