David,
I am doing exactly what you want to do (except I am all wireless g).
In my 2nd floor office, I have a Linksys wireless router (WRT54GL).
I am using
this ethernet bridge in the basement home theater (supports WPA).
I have
a Linksys 8 port switch plugged into the bridge.
Then I have a 3808, PS3 and Wii plugged into the switch. Everything works great.
Note - I got a more powerful set of antennae for the router from Radio Shack and the signal strength improved dramatically.
Not sure why you want to introduce wireless n beacuase g has been just fine.
