I would guess that with some sort of Y adapter you could attach two displays, however you would get the same image on both displays. Think of an audio Y adapter, you get the same sound on both displays.
I have seen solutions with the express card slot, but they aren't cheap and they don't offer full resolution.
If you want two displays, you use the one on your MBP and the other external attached to it.
Or, you buy a Mac Pro, iMac, or even the new Mac mini. Actually, the Mac mini may be your best solution as far as getting two displays to work but it cannot be two 24" ACDs. As it only has one mini display port. If you want two 24" LED backlit ACDs, your only choice is the Mac Pro with TWO GRAPHICS CARDS. Any current solution has one mini display port per card. On the other hand, you could connect up to eight 30" ACDs to a Mac Pro Early 2009 with 4 graphics cards.
Good luck.