I need some advice on buying a gaming laptop

Notebooks such as the Alienware M15X and M17X and the Dell 1730 have better gaming performance because they both have the most powerful video card currently available for notebooks, the Nvidia 8800M GTX. Asus doesn't use top-end mobile video cards in their notebooks because they run considerably hotter and take much more power than midrange/performance mobile video cards.

If you've already been looking for several weeks, I'd advise you to wait a few more. Intel's new chipset is due out in June and would allow more upgradeability than the current one, and neither ATI or Nvidia has come out with a suitably upgraded mobile video card yet this year (they tend to put a newer and faster version out each year), so I'd expect better video cards with similar heat and power requirements to be released soon.

However, if you can't wait-
all of the notebooks you selected should have very similar gaming performance, since they all use comparable graphics cards and processors. The amount of dedicated video memory only makes a difference when the graphics card can utilize more than is provided. Neither the ATI 3650 (a revision of the 2600) or the Nvidia 9500M GS (a revision of the 8600M GT) have the power to use more than 512MB of dedicated video memory, so the extra amount of video memory in the ATI card won't help you. I'd suggest looking at the other features of the notebooks to determine your preference. For instance, 2 of your selections have 15.4" screens and 2 have 17" screens. The notebooks with smaller screens will be more portable but the ones with larger screens also have higher resolutions so they'll show more detail and allow for better multitasking. Also, design is a factor. The G series is designed to be attention-getting, while the M50 & M70 look more professional.

Tech Fuzz is the best site I've found for upcoming computing information. Upcoming mobile graphics cards are on the top of the page, scroll down to June for Montevina info