Windows has no idea what the Mac's HFS filing system is, which is why it can't read it.

You'll need a program that will let you browse the drive - not done this for a while, and can't remember what I used, but I expect Googling "Browse Mac hard disk on Windows" will find you some nuggets of information.

Better idea:

Get a new hard disk for your Mac (they cost pennies), install OS X etc, then plug your old drive (still in the USB cradle) into the Mac.