With the card, all you need to do it boost the power output on the router, I personally boosted it to 251mW, however I wouldn't recommend you doing it as I don't want to be held responsible if anything happens to your router, however I take full responsibility for my router!
EDIT:
This is the antenna you are looking for:
http://www.microwarehouse.co.uk/catalogue/item/LKSWL054