wrt54gc and xbox live

anyone have any ideas on how to get an xbox live to update over the
aforementioned router? it can see the router and passes every test up to
getting an update and then fails...

I also have problems with a linux install getting past the router on to
the net. As I'm a complete linux newb it's entirely possible that it's
some setting, but the fact that both linux and the xbox can't connect to
the net but can to the router screams "I've overlooked an important
setting" to me.

Many thanks in advance