The solution is to use both the Number Lock and Fn keys.
* First, the Number Lock must be on. (On my Inspiron 9100 it's located above the F11 key: 'Num Lk') There's a light that turns on when you activate it to show you that it's on. (again, on the 9100 it's the first of 3 lights above the keyboard, and to the left of the power button. The icon below it is tiny, but it's got a 9 inside a lock - thus Number Lock). Once number lock is on ...
* Then hold down the blue Fn key (second key in from the bottom left of the keyboard, right beside the Ctrl key: 'Fn' written in blue). Hold the Fn key down with your left hand (I use pinkie or thumb, actually) and type the number pad keys (also in in blue) with your right hand. (So M=0, J=1, K=2, etc.).
Just remember, you have to keep holding the Fn key the whole time or you revert back to letters.
Hope this helps, and Happy Numbering!