QoS-Xbox Live-Download help!

[euphoria24]

I have a linksys WRT54G router with tomato firmware

Can anybody guide me on how to use QoS so that I can play xbox live while downloading music without it lagging? I am on Rogers Express and there must be something wrong with what i am doing. The internet speed should be fast enough so it wont lag.

Would i have to switch from Tomato to DD-WRT for better results?

Any help is appreciated
Thanks

[user01]

Something to do with Port Forwarding.