If you want a good gaming computer for around $1400 I would heavilly recommend that you build so you get your money's worth (especially since you want a LCD). But if you really don't want to build it yourself you should select a custom build from monarch computer.Since you need a LCD monitor (~$200 minimum), Windows XP ($90), and Microsoft Office 2003 ($130) your budget for the actual computer would be something like $1000 dollars.
If you do decide to get it from them I would recommend these parts:
AMD Athlon X2 3800+ CPU (get one with a CPU fan)
MSI Neo4-f motherboard
Antec Truepower 2.0 550W power supply (might be a little pricey but worth it)
7600GT video card (mid-range card but will play Doom 3 and BF2 fine)
I would also grab 2GB of RAM (especially for BF2)
Windows XP Home w/ SP2
Don't select Microsoft Office from them either, you should just order it seperate from Newegg or someplace for cheaper and install it.
The case, optical drive, and hard drive are up to you.