Look here:
http://www.subsim.com/radioroom/showthread.php?t=195438
or here:
http://www.subsim.com/radioroom/showthread.php?t=194766
Those two tools are very easy to use, I tried them both, but the one from subsim download section is ... meh :P
And you didnt say if your Win7 is 64 or 32 bit? Your CPU is.