Yeah, the Gameboy DS (DS standing for Dual Screen if you don't know it already) seems much bulkier than the SP does. I really don't know why they'd still sell the SP since the DS can play Gameboy Advanced games too(hopefully the other Gameboy games too). Maybe because it's a cheaper alternative? (like the GBA and the GBA SP)
To compare the two coming handheld systems, Nintendo's Gameboy DS and Sony's PSP (Playstation Pocket), I say that the DS is gonna be more worth it. First is the price. The Gameboy DS will start out at $150.00 while the PSP will be expected to start at $250.00. I wouldn't pay that much, even for a game system! A $100.00 difference is huge. The Gameboy DS will still use cartridges, which have been really reliable in strudiness and it doesn't need a memory card. The PSP will use some sort of mini-disk, which means sensitive games, especially on the road. And they will have to add a shock protection for continuous play, which can add to the cost. Because the PSP uses disks, it needs a memory card. For portability causes, more parts means more trouble. The DS has two screens, one touch sensative, while the PSP has a slightly larger single screen. Since the PSP has graphics slightly less comparible to the PS2, it needs a really good screen to play on. I've played on some portable screens, and everything seems blurry.
