Question about gaming desktop?

I want to get a good gaming desktop to play good games on, mostly shooters like battlefield and medal of honour. What kind of specs would I need to run a game like this. Should I buy a pretty good gaming pc and upgrade it but graphics cards are very dear, how good of a grahics card would I need for games like them and for online games. Or should I get a very good one but dont upgrade and how much would this cost?

please help and give links,Question about gaming desktop?
Specs for Battlefield Bad Company 2



Minimum:

OS: Windows XP

Processor: Core 2 Duo @ 2.0GHz

Memory: 2GB

Graphics: 256 MB Video Card (GeForce 7800 GT / ATI X1900)

DirectX庐: DirectX 9, 10, and 11 support

Hard Drive: 15 GB



Recommended:

OS: Windows Vista or Windows 7

Processor: Intel Core 2 Quad or higher

Memory: 2GB

Graphics: 512 MB Video Card (GeForce GTX 260/ ATI Radeon 4870)

Controller Support: Support for Logitech G15 and G19 keyboard LCDs in multiplayer



The cost depends on how you do it, if you pay someone to build it, it will cost a lot more, you can build a desktop yourself and it cost roughly $800, if you pay for someone else to build it, the cost can be substantially more.



as for a laptop, i would look at ASUS they are the least likely to break



the laptop in this article runs about $1750

http://www.detecht.net/Article.php?id=8



as for alienware, they have really gone downhill since Dell bought them, nothing against Dell, i have a Dell that i love but i just would avoid alienwareQuestion about gaming desktop?
CPU: Athlon F57 (or a 3700+, or maybe a Dual Core 4800+).

Memory: Gskill 1Gb Low Latency TCCD (2-2-2-5 timing at 200Mhz)

HDD: 2 Raptor in RAID for programs and 160Gb SATA hdd for data/back-up

VidCard: 2 GeForce 7800GTX in SLI

Well its gonna cost 2000 - 3000 dollars. You migt wanna consider getting a alienware M17x laptop for bout half the price it runs games amazing but has no internal hardrive.