Following on from the comments about connecting to xbox live with the microsoft wireless router. I had the same issues, tried everything i could find online (upnp, firewall ports etc.. and checked with belkin.)
turns out you need to manually configure your DHCP settings on the dashboard, even if your IP is dynamic. This is even more annoying because it is the complete reverse of what xbox support tell you to do.
Apart from this (which very nearly claimed my sanity) i had no issues and the product works like a charm with both pc and xbox and DS.