Good luck finding a working wireless n range extender.
You can fine 1 but wont work though "tons of walls".
I first tried power-line: http://www.newegg.com/Product/Product.aspx?Item=N82E16833122233&Tpk=NETGEAR%20XAVB101
That got me up to 3MB/s and I could finally play games without lag and watch 720p HD. With 30 seconds of loading though and no way in heck it could play 1080p, would have to re-buffer every 20 seconds or so.
What will work is this bad boy: http://www.newegg.com/Product/Product.aspx?Item=N82E16833122243
Assuming you have cable?
I've been using a par since March 27, 2010 and could not be happier. My router is 1 floor down and over 10 walls away from my bedroom.
With this bad boy I now get 8MB/s. Yes that is megabytes. Before with just my 655 router I was lucky to get around 1MB/s and could not play games or HD at all due to drop outs and 5 minutes of buffering. uTorrent would also kill it instantly.
Now I have no issues maxing out my 16mbps/2mbps connection.

No lag, no buffering. Plays 1080p perfect. In fact I can transfer a file at 5MB/s from my computer to the router and still watch a 1080p BluRay video at the same time without any lag or bugger thanks to the 655 smart QOS. Highly recommend you set that up right now!