The DS Lite will rumble away while you play, but the RumblePak that you have to use is less than optimally sized.
Instructables user Xyzzy has found a solution to that problem, hiding the pack in the dust cover for under cover rumble. The mod uses an old Pokemon cart, a Nokia 5100 motor, and quite a bit of creativity, but if you’ve got some excess skill in the electronics department, it might be worth checking out.
[Instructables - DIY RumblePak for Nintendo DS Lite]
[Via: Nintendo Gal]