[ora]

From http://support.apple.com/kb/HT1515?viewlocale=en_US

Question: Can AirPort Express act as a bridge?
Answer: AirPort Express can act as a bridge in three different ways:

If you have an existing wired network, it can bridge this network to wireless clients.
If it is set up as a WDS remote or relay station, it can bridge the wireless network to wired clients.
If it is set up as a WDS remote or relay station, it can bridge the wireless network to wireless clients (or "wirelessly extend" the range of the network).

So maybe it is possible, though cheaper to use the XBOX wireless adapter I think. I never tried mine in bridge mode, and am away from home at the moment, I may try it when I get home and I'll let you know but it may be a while.