Signal loss

Having a bit of trouble hooking up a third computer in the house. Access point is on 2nd floor. One computer on same floor works fine with a USB wireless network card (Dlink DWL122). Tried setting up the third computer in the basement the same way. It's detecting the network, but not maintaining the signal. My tech said that it could be because a)the USB ports are older (1.0); b)it has to go through 2 floors; and/or c)too much interference (including a home security system)

He said to try an internal wireless network card; get some type of booster to amplify the signal; or run 100ft of ethernet cable down. Obviously I would prefer not to run the cable, but does anybody have any hints as to what might help. Thinking also of hooking up a directional antenna. Trying to keep costs reasonable as well.

Thanks Rod

What is the orientation of the antenna? If both are vertical try laying either or both horizontal with the same orientation not 90 degrees to each other.