Post by Domh
Well, your framerate would be affected by your computer's hardware, but unless you have a major issue somewhere your lag shouldn't be affected by the hardware (noticeably anyway).
Your lag will be affected instead by things such as your ISP, your ISP's network conditions, whether you're on wireless, are you sharing your net connection, are you downloading anything while WoW is running, whether your computer is harboring a small army of viruses, etc. Really the only difference you should see in lag should be a function of the software you're running, such as a cheap firewall might add a few ms of lag, or you might see some small changes across operating systems.
What I'm trying to say here, is that lag spikes in arena shouldn't be a result of your hardware, but for the most part outside factors.
As for other things to look for, I'd suggest an ATi or NVidia graphics chip. What you want to look for in these is the second digit of the number. The first digit represents the cards series, but the second digit represents the card's performance class. For example my old laptops ATi Radeon 2600 HD will trump out my roommate's ATi Radeon 3100 HD, as it's a class 6 in performance over his entry level class 1. This is a dimishing return though, and in a choice between a 3500 and a 4400, the 4000 series would likely win. I strongly recommend that you look for something in at least a performance class of 5 if you want to keep your graphics settings turned up in the next expansion. Additionally, don't fall into the idea that more video RAM is always better - while this was once the case it hasn't been true for ages. I suggest you keep it to 512MB or higher on the graphics card, but if all you're doing is playing WoW on a laptop resolution screen, this should be more than enough. In most laptops, if need be it'll boost your video RAM from your main RAM if it has to, with only a small performance hit.
If you're going to be gaming on this a lot, and not using an external screen, I'd also suggest looking for something with a screen in the 15" or larger range. A small screen on your main computer is just asking to be annoyed. A HDMI or DVI out (or DisplayPort if you actually find a laptop using it) will let you use a larger external screen if you want to upgrade it in the future.
In terms of processor, in your range for a mobile computer look for a dual core chip such as a Intel Core 2 Duo in the 2.0 Ghz + range (Mobile processors tend not to be quite as speedy as their desktop counterparts in the same price range, but my own laptop is only a 1.66Ghz dual core and handles dual boxing WoW well enough on moderate graphics). An AMD Athlon X2 might work as well, but I haven't really looked into AMD's product lineup lately.
Also, if you're going the Windows route, as I assume you are, do not skimp on your RAM. Vista and to a lesser extent Windows 7, really, really like the RAM. 2 GB should be your minimum, and I'd suggest 3-4 or more if you can swing it (though watch out, as if you go with 4 or higher, only slightly over 3 will be available if you have a 32-bit version of Windows instead of a 64-bit one).
And as a final parting advice, I'd suggest staying away from HP and Compaq systems. They're good while they work, but I have yet to meet someone who's had a HP and hasn't been massively screwed over by their warranty service and support (On a home system, their business support is actually decent). I tend to favor Toshiba myself, but Dell, Asus, Gateway and several other brands should do fine.
Something like
this would likely fit the bill of what you're looking for.