Q: How do I get DirectX10? My video card supports it and I want to use it.
A: It is ONLY available in Windows Vista. You'll need to upgrade to Vista if you want to use DX10.

Q: I have a lot of games installed, but I've lost the original manual/envelope so I lost the install key. Is there a way to get the install key back from the installed copy on the hard drive?

A: Maybe, you can try Game Key Revealer, which supposedly works on over 500 games for the PC (sorry, not available for the Mac yet).