Try a line speed test like the ones at dslreports
. It is more than likely your internet speed is slow not your wireless connection. Another thing you could try to rule out what is causing the speed issues is run a ping command. If you are using xp go: Start> Run> type cmd and press enter. Then on the command line type ping 192.168.0.1 (thats assuming that is the address assigned with your router, which is the case with most routers... if not try 192.168.1.1) and watch what the ms time response is then do the same thing but ping a site like google (so: ping www. google.ca ) the google ping should be significantly more than your router ping, which should be around 1 or 2ms. The same thing should be doable in vista, just type cmd in the start search box.
Ah yes, forgot about signal strength. Check your signal strength in the system tray as well, a low signal can lead to slow sluggish performance. If this is the case, try moving the computer/router closer to each other, or obtain a more powerful antenna (you could even look into wireless range repeaters, available at places like staples or best buy)