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First - take a closer look at your laptop keyboard. Nearly all of them have a double keyset (usually somewhere to the right of the keyboard) where if you hold down a function key you can access the numeric keypad. Personally I find this method annoying as typing numbers now requires both hands or constantly locking/unlocking.
Second way as someone else suggested is an external numeric keypad. I keep one of these in the laptop case, I got it at CompUSA for around $15 - $20 and it connects through USB. Does the job.
The third way is through one of those new "fruit roll up" style keyboards (my own name for it). It's a rubber keyboard that rolls up and can easily be stored in the laptop case. Hook that up and you now have a standard 104-key keyboard with center arrows/insert/home/pageupdown/etc. buttons, and a numeric keypad. With full sized keys too. I didn't buy one of these, but borrowed a friend's ... it's a nice keyboard and easy to use but using an external keyboard requires SPACE - I usually use my laptop when I'm not at a desk.
Or your alternative is to get a laptop with a full sized keyboard, but they're on the expensive side usually. It would be worth it if your primary PC *is* your laptop, but if you're only an occasional mobile user like I am it's not worth the extra cost. The external keypad works best for me.