speed up a wireless connection

Sup guys. I just changed my whole home network to wireless. Everything looks ok so far and all the computers close to the router seens to get a good internet performace. I just got one big issue: One of the computers is in another room, and because of that both the network and internet connection there gets extremelly slow.
I have cable modem and using a Wireless-G router 2.4 Ghz with speed boost. All the network pci adapters on the pcs are wireless-g 2.4 Ghz. The computer in the other room is aproximally 30 feets away from the router.
Any idea how can I solve this problem without have to move the router or the computer from their position?

 

Possibly This?

 

Is this antena better then the one that comes with the pci adapter or somethin like that?

 

i believe it is. i g2g to a bb game somone will help u out more

 

Not the issue, but if you have a 2.4Ghz cordless phone, that can cause interference and drops. Seems you whole wireless is 2.4 so I thought I'd pass that on.