I'm a new owner of a Y400 and overall, I am very pleased so far with the performance of this computer. It has many earmarks of a well-conceived design for its category of computer.
That said, while recently trying to type alt codes in my word processor so I can produce special characters (e.g. so that I can type 'resumé' instead of 'resume'), it appears that Lenovo didn't see fit to include the ability to:
enable num lock or
give access to an alternative numeric keypad by doubling up keys using the FN key (on other laptops of comprable size, the keys that do double duty for a numeric keypad are 789uiojklm)
I've been really hoping that something in that article will enable me to be able to use alt codes as needed without the need for an external usb numeric keypad but I haven't been able to get any of it to work on the Y400 yet.
To enable the numlock function in the Y400, search for on-screen keyboard in Start.