For GW2, if you want to play it at resolutions of 1680x1050 with some additional settings turned on (Anti-Alias, etc.) I would recommend a laptop with at least Nvidia Geforce GTX 260M/280M or ATi Radeon Mobility 4850/4870 GPUs. Even these GPUs may not be able to handle the persistence world with a lot of people on screen at once from looking at GW2 trailer and graphics detail. Might have to tone down the display resolution just to get playable frame rates with some medium to high graphics setting on.
CPU and GPU almost go hand and hand together. If you have a super graphics card paired with an avg CPU then you'll get performance bottleneck with games. For laptops I would be looking at 2.5GHz CPU and up. And I wouldn't bother with Quad Core and just focus on a fast Dual Core with minimum of 4GB worth of DDR2/3 memory.
I've actually been looking into buying a new gaming and all purpose laptop myself recently. The Sager NP8662 seems to win in all areas and based on buyer reviews. It's 15.4" and decent screen resolution and GTX 260M 1GB GPU.
http://www.xoticpc.com/sager-np8662-...wconfigure=yes
ibuypower.com and cyberpowerinc.com also have a similar 15.4" laptop using the same Clevo motherboard with onboard "3D" audio/sound card and HDMI out port. It looks good too, not overly fancy. With the Sager model you can get all the latest BIOS, drivers and customer support through them otherwise you can get the latest drivers from Clevo's website I believe. I think Clevo already has Windows 7 drivers available for the motherboard model should you want to pay extra for the upgrade or get it free (mail-in-rebate offer). All these websites offer some kind of 3-5% and military discount so just look carefully when customizing to your need.
I don't own Alienware products and am unsure how often they provide software (BIOS, firmware, drivers, etc.) support update. I do own a Dell laptop and I wouldn't recommend Dell for gaming laptops as they do not provide GPU driver update often if ever. With some brands you can go directly to Nvidia or ATi to get the latest laptop GPU drivers without fear or incompatibility issues.
When looking for laptop the first thing I'd research on is if the laptop you are interested in has motherboard chipset, audio/sound card, and GPU drivers for Windows Vista or 7 (future proof) from manufacturer or the manufacturer allows for direct driver updates from the parts manufacturers (Nvidia, AMD/ATi, Intel, Asus, Clevo, etc.). Again, some manufacturers use customize or propriety software (drivers, firmware, etc.) and don't allow for updates from 3rd party which in the long run is terrible for the buyer. I think this is a way of preventing future proof even though possible (fast CPU, GPU, etc.).
Think of the size you want then go from there by component comparisons and price. Personally, anything bigger than 15.4" even 15.6" screens are too big to be considered portable due to space needed. 15.6 is about 1" longer than 15.4" width wise when I visually compared two Asus models at a local Best Buy. Good luck.