Line of sight ok? What brand of router/wireless card do you have? Are you close to your wireless router, or are you moving around the house when it is dropped?
Brand of hardware is important. Sometimes you can find firmware updates and improved drivers (or third party drivers) that are far better than what the hardware comes with.
I ditched my D-Link drivers my card came with for real Atheros drivers and it's alot better.
how far away is the router from your computer? when you do have a connection, whats the strength? and what type of wirless network is it? (802.11a/b/g?)
most likely its a hardware issue, i know i wasnt able to connect my belkin wireless card to my friends d-link or lynksys (dont remember which). Try finding hardware from the same manufacturer.