Yeah, the Leonardo is a fussy one. First thing I can suggest is to try another USB port. Not all USB ports are made equal when it concerns Windows.
Second is to find a USB hub to test for stability. I noticed that with my Leonardo, it would hang during the sketch upload. When I switched to the USB hub, that eliminated that problem. Also, make sure you have all your Windows 7 updates.
Lastly, try eried's modified IDE. It is pretty slick with the driver installation.http://arduino.cc/forum/index.php/topic,118440.0.html