If you purchase a directional antenna you need to change your transmit and receive antenna to the same. Or purchase a wireless antenna with diversity meaning two TNC connectors.
You might want to think about purchasing another wireless adapter. PCMICA wireless cards often are subject to damage.
Changing your wireless transmit power - You can change your wireless transmit power but it comes with a price. First this will cause your wireless router to work harder and heat up more thus reducing your wireless routers life span. Their is no need to have transmit power over 70mw for a home or small office. You can crank up your transmit power but remember more of you signal will bleed out into the street giving war drivers another target.
You will know if you are having interference if you are constantly connecting and reconnecting to your wireless network. The first thing to try is to try and change the channel to 2 or 11 or what ever works. Next you can make or purchase a wireless directional antenna to focus your signal where you need it. Third Move your wireless router to another place in your home. Fourth boosting your wireless signals transmit power has it’s benefits and it’s consequences, you could fry your wireless router and it could give you hacker issues. Finally if all else fails go out and purchase a new wireless MIMO router.