PC wont connect - Mac will

[Joe 90]

I've no idea of whats going wrong so I'll try and explain what i've got here.

Our network consists of our BeBox downstairs which is our main router connected to the phone line. This has one of those plug network port things which runs up to the first floor where I have a switch which serves;
- Mac
- PC
- Xbox
- DD-WRT router

My 2nd router is only connected through the LAN ports in order to boost WiFi & connect my xbox on the floor above.

The problem which I can't figure out comes from Windows Vista. As you might expect! OS X works fine, connects to the BeBox downstairs over WiFi & Ethernet. However today I've noticed that the PC has issues. I don't know whats changed, its been working fine for weeks. But in network connections its got 'multiple networks' and picks up the gateway for the BeBox but a local only connection!

I think I can see the problem. The PC's ethernet is picking up a connection the the DD-WRT & its wifi is on the BeBox. However if its on the bebox, I'd have thought it'd pick up the internets.

I don't really know where the fix is, but would like to get my mac back to being my mac which people are too afraid of to use...