Just wanted to report that something has improved with Airport and now our linksys wireless B game adaptor works again with XBox Live.
Don't know if this was the most recent Airport update or the fact that we are using the Airport Express for our wireless connection (vs. our iMac as the software base station.)
Thought my son's subscription had expired but it must have a little more time left on it. The last time this all worked was with 10.2.8.