Notebook Adapter slow or not connected

I have a Compaq Presario 2100 notebook, AMD processor, 512 RAM, and XP. I am
using a Belkin Wirless G router and a Linksys WPC54GS Wireless-G Notebook
Adapter with SpeedBooster. The problem I constantly have is that I have
problems connecting, problems with speed, and I fail to pick up available
networks. At home I have to usually plug in the card and unplug it multiple
times before it will pick up my router and connect. On rare occasions it
picks it up right away and connects. It also drops me on occasion. Once I
am connected, I might as well be using a dial up connection. Even when it
tells me that I am connected at 54kbps, it almost never does, I still have
problems loading web pages. If I try and download a anything it moves at the
speed of dial up everytime and on large files almost always drops the
connection. When I am out around town I have the same problems picking up
other networks. My wife has an almost identical computer but hers has a
built in card. She never has a problem connecting to anything, picking up
networks, or downloading at high speed. Does anybody have any idea what may
be causing this or what I can do to fix it.

I recently had to do a complete reformat due to a system crash. I actually
thought things would work better because I had fewer programs installed on
the computer and was better updated on my software but it is exactly the same
now as it was before.

Also, I am using both the windows firewall and Norton. I have tried turning
these off, but did not notice any real difference. It is kind of hard to
determine if that worked because you can never tell when the computer is
actually going to pick up the network and connect.