I struggled the same way when I moved into the one room of my house that seems like a faraday cage. In the end I ran a cable down the siding after tapping the base of a window.
But onto your problem. Remember if your on N that 2.4 Ghz penetrates better than 5Ghz despite local interference. Directional high gains will probably serve you a little better than a unidirectional. But remember if its only on one router the effect isnt great in both directions. But keeping the main router effective for the rest of the house also means not messing too much with its antenna's.
Assuming you have a router that lets you configure bridge and repeater? I run custom firmware so its been a blessing not to have to buy more hardware. My main solution was to move the modem and router to the top of the house in the hallway and put a repeater bridge for everything on the bottom floor. Remember with a repeater your wireless latency will be about double, this should be okay for conferencing but not for gaming. So your gaming desktop is probably centered around this entire network schematic.
Most routers and wireless adapter use 10% or even less off the maximum power allowed. Check out Ubiquity's 1000mW solutions -
Amazon.com: Ubiquiti Wifistation USB Adapter 802.11g/n up to 1000mW: Electronics They mostly carry commercial products but they did/do have home products. I cant really find them on their website since they did the redesign.
I know this info probably isnt of much help. But ive been through it figured id share some observations.