If i were u i would go over u network an ensure the follwing:
1. if its wireless that its got a key and billy n his mates down the road rnt getting free internet
2. go over each machine xbox pc and the router and make sure all network names are set to somit indiviudal.
3. if ur networks routers IP is 192.168.1.1 set ur xboxs manually for IP 192.168.1.2 and set the DMZ of ur router to the xbox ip x.x.1.2 then (that way u will still be able to host games on xbox live ;-)
4. set the pc to ip 192.168.1.3 or set for dhcp ;-)