How to I extend my Wireless Range?

The 2WIRE modem AT&T provided me works great, when your in range. Because, to tell the truth, the WiFi range on those things suck. I bought I wireless repeater/extender, and it did extend my range, but it slowed down the WiFi connection on ALL the devices in my house significantly. My PS3 and Wii are too far away and I need them connected. Can someone please help?