Apple Keyboard with Numeric Keypad on Windows-7
Hah! I actually use a mac keyboard as the normal keyboard on my windows boxes. I like the laptop-feel and the aluminium.

This is easy to fix. 

Push "Clear".

The "Clear" key on the numberpad gets mapped to the "NumLock" key on windows.

If you want to fix the swapping of the alt and "Command" keys, KeyTweak works well.
It can also let you set the additional F-keys (e.g. F13-F19, which are not real F-keys) to be  whatever you want. I have them mapped as media keys (next-track, pause, etc...)