I think that's the maximum, unless youre using good BIOS such as AMI, then you can configure as you wish. But let me remind you about integrated graphic card, especially notebook. No matter how much you set the memory, not worth it. Even Intel GMA 950 or ATIXpress200 pumped up till 1gig also perform nothing.
If you want then you might upgrade to X1300 or 7300, ask dell about it. Im sure they have this option but they will charge you more...