Are you using a wireless modem? Or are you connecting to a access point? Because if you are already connecting to a wireless access point with your usb adaptor, chances are you can easily connect another. Also, some wireless modems even do the routing for you, such as those 2wire combos.
However, if it is a remote location your connecting through, a router isn't gonna help much, cause you'll need a local connection to connect to.
One way I've gotten around that was to use my usb adaptor to pick up the signal with my server, then i route out to my router using internet connection sharing where it can be split to any other comps I got laying around.
I also second that ad-hoc=bad.
hope this helps