Wireless Network question

My wireless network router is in the basement of my house along with a few computers and the cable modem. I’ve just added an XBOX 360 on the first floor media room and got the USB wireless adapter. The problem is it’s not finding the network. The 360 is about 50 feet away and one floor up, so I’m thinking it’s a signal strength issue. My PSP can connect from the same room as the 360 but it’s a really weak signal that drops easily. So I’m thinking of adding a directional high gain antenna to my router in the basement. Should that make a big enough difference to give me a decent connection on the 360?