Supplement to iBook Antenna?

[Ghengi]

I have an iBook (Airport Extreme card) connected to a network via a D-Link 614+ wireless router. The connection is fine when I'm nearby, but when I take the iBook downstairs, I lose the connection almost anywhere in the house except for near the base of the stairs. (It's an old house with plaster walls, but I think it's more the iBook's antenna that's the problem--a borrowed PowerBook that we had here seemed to have a more robust connection.)
I'd like to get a directional antenna to attach to the iBook (not to the router). None of the compatible D-Link antennas have USB or Firewire connectors. (They have SMA or TNC.)
This is for my wife, and the whole reason for going wireless (using a router my son bought for his PC) was to allow her to work from different parts of the downstairs. We could attach the antenna to the router, but then she'd have to go upstairs and turn it every time she moved, instead of just taking the antenna with her.
Any ideas? (The iMac and PC upstairs are wired to the DSL modem upstairs so moving it downstairs would create new problems.)

[mdnky]

Verify your antenna cable is properly connected to your airport card before you do anything else. A lot of people have had issues with them not being installed properly (ones they install themselves as well as factory installed ones) and aren't getting any range because they not actually using the antenna.

Apple's iBook G4 airport install instructions

[Ghengi]

That must have been it. Ironically, I had disconnected and reconnected the antenna the night before, when adding a memory chip. Everything works fine now, but I probably wouldn't have tested it downstairs again before wasting a lot of time pursuing another "solution."
Thanks!