Help/opinion on setting up another wireless network in my house

My current modem and wireless router are hooked up in the basement of my house. When we watch movies via Netflix and or stream through Apple TV upstairs, the movies/shows often lag and or time out. We have a lot of devices sucking the bandwidth, but I always shut them down if I know we are going to watch a movie or play on XBox live (everyone knows you can't lag playing MW3 or you'll get pwned!) Anyway...would there be any issues with setting up another wireless network upstairs in my house? Any and all opinions are welcome.

BTW...I've run my own connection speed tests on all 3 levels of my house: basement averages 17 mbps, main level 8, and upper level 2-3 mbps....