Seeing as the 8800m GTX is a mobile part, I wouldn't be surprised in the least if it performs worse than the desktop version. Heck, I'd be impressed if it can match the 8800GT in performance. Dell is known to underclock their cards so they play nicely in the confined spaces of a laptop (I still have the original 7800go in my laptop). Hopefully nvidia is using the new 65nm process and as many stream processors as possible.
Guess we'll all see next week (not that I'm in the market for one, but I like to stay in the loop).