I have clean install of Windows 7 x64 with two SATA hard drives. When I open My Computer, I can see only the drive where Windows are installed (and all partitions), but I don't see the other one.
When I go to disk manager, I can see that both drives are detected and the one that I don't see in My Computer is also marked as Primary, but when I right click, the Open and Browse are gray.
I also checked drives with gparted on live Ubuntu and they both seem to work correctly, the second drive wasn't marked hidden or anything else. Before installing Windows 7, I had Windows XP, where both drives worked properly.