Some versions of the Linksys WRT54G support third party firmware, such as dd-wr
t and/or tomato
. So if yours is one of them, you could install that firmware and configure the router as a wireless ethernet bridge.
<-- 3g -->[droid phone (wifi ap)]<-- wireless -->[wrt54g (wireless ethernet bridge)]<-- wire -->[desktop]
Of course, I'm assuming the WRT54G is not presently being used as your primary router.