Weak wifi signal upstairs; time for a repeater?

[StupendousMan]

We live in a two-story house.  In the middle of the first floor, we have an Apple AirPort Express connected to our fiber-fed network cable.  It works fine -- laptops on the first-floor get great signal.
 
Upstairs, my wife and I each have an office with a desktop computer.   My desktop is an oldish box running Ubuntu.  The machine didn't have any wifi receiver built-in, but my wife found a small USB receiver in her junk drawer and, after an hour or two of configuring, it worked.  The problem is that the signal is weak, and transmission is slo-o-o-ow: some ten times slower than a laptop in the same room.
 
One option is to purchase a better receiver for the desktop machine, but I worry about getting one which will have drivers compatible with Linux.  Another option is to keep the receiver, but purchase a wifi repeater/extender for the second floor of the house.  That would have the added benefit of giving my wife's computer a better signal, too, I suspect.
 
Any advice on the situation, or recommendations of particular hardware?
 
Edit: no, I can't run a cable upstairs.  The Stupendous Woman has declared that there will be no holes drilled in any floors or ceilings.

 

[VORP Speed]

http://sonsofsamhorn.net/index.php?/topic/85712-Extending-Wifi-Range


See the above thread. I got one of the powerline adapter systems for a similar issue and it's been awesome.

 

[StupendousMan]

 
I know next to nothing about these things, but the bolded seems to suggest it's an issue with desktop, no? Either the USB sucks (which it probably does if she "found it in her junk drawer") or just your "oldish box" being older and slower than you might be willing to admit? How does the signal on a laptop in the same room compare to the signal the same laptop gets downstairs? 

 
*slaps forehead*  That comparison of laptop upstairs vs. laptop downstairs is something I should have done earlier.  Thanks for suggesting it.
 
The result is .... that the laptop can transfer a 10 MB file in the same time upstairs and downstairs, and the wifi signal strength is shown as "5 bars out of 5" in both places.
 
This points to a crummy USB receiver being the main culprit, rather than a weak wifi signal.  Maybe I should try purchasing a better receiver instead of a repeater.

 

[derekson]

I was going to say that an Airport Extreme that is reasonably centrally located in a 2 floor house should cover the whole house pretty well. That's my setup and I get wifi past the edges of the entire 1 acre+ lot. I did move the router to the 2nd floor when i rewired the cable a few months ago which did improve things a bit generally, FWIW.