Yes. The DS Lite does indeed have a slot which holds gameboy advance cartridges. You slide the cartridge into the slot only one way. You will know if it is in the right way.

when you turn it on i am guessing instead of loading up the ds game it will load up the gameboy advance game. it does work. my friend's done it, and shown me it, but he did not show me the loading sequence. i think you turn it on, and you have to do the touchscreen thing where it says start or whatever, and then instead of loading up a ds game it will load up the gba game, but at the beginning it still has the ds menu. it's *not* automatic.