trouble bridging dlink 615 d2 (from virgin) with standard sky broadband adsl wireless

so we currently have sky adsl broadband with their standard wireless router in our house. This is on the middle floor and there is no way to move the phone wires etc. I have a dlink 615 revision d2 wireless router which i would like to use downstairs so we can connect our xbox to the internet. I believe i need to set the dlink to be a wireless bridge? I have flashed it with the latest dd-wrt firmware, which has worked but i think i maybe getting some of the settings wrong as when i plug it into the xbox it doesnt connect to the internet. I believe this is possible but seems quite tricky and was wondering if anyone had done this before or knows of some instructions? I know we could easily just go pick up a xbox wireless adapter but would like to try this first, its a bit more fun!