what exactly will you be using it for? The laptop option (for nearly all cases) should only be considered if you want to take it beyond your home. For the same overall features the price difference between a laptop and desktop is around $500 (more for a laptop).
If it is only a "home use" computer then why not get a desktop pc? If you need a semi-mobile desktop pc, then why not get a mini-tower pc like this one?
With Dell, I would highly highly suggest only going with their xps line. They cut too many corners on their lower lines. My six-year-old xps dell is still kick'n (with NO problems) while I'm having to literally reconstruct my 1.5-year-old 8400 dell due to motherboard inadequacies.
Also, if you want a gaming system, you will want a system that's easily and cheaply upgradable. Laptops are neither. Remember, there's always some new hot game on the horizon that has ridiculous hardware requirements.