New computer system specs... how will they effect PS?

[FalconFC]

I am looking to upgrade my current PC to one that can stand for Several years and be powerfull enough to this years and next years most demanding games (mostly FPS e.g. half-life and Doom3).

Currently my most demanding game is obviously Planetside (until Half-life 2 that is). I want a system that can easily take on MAX detail and MAX settings for PS. I am leaning towards an Alienware system with all those lovely goodies and huge system specs. Here are my current specs (everyhting on PS is turned down low/off except for the tickable options on the graphics page).

Processor: AMD Athlon XP 2000+ @ 1.67 Ghz
RAM: 512Mb DDR 333Mhz
Graphics: Geforce 4 MMX 440 64Mb
Hard Disk: 16Gb 5000rpm
DVD: 6x speed DVD-ROM drive
CD-RW: 2x speed CD-RW drive
Soundcard: SB Live! 6.1
Moniter: 17" CRT moniter capable of 110 Hz
Mouse: Logitech Wheelded Mouse (Bail and Chain style)

Now here is what i plan on upgrading to (i've spent a while saving up and have an EXTREMLY big budget):

Alienware
Processor:P4 3.4 Ghz Processor
RAM:2Gb DDR SD PC-3200
Graphics: ATI Radeon 9800 XT 256Mb
Hard Disk: 120Gb 7200rpm
CD-ROM: 16x DVD / 52x32x52x CD-RW Combo
Soundcard: Creative SB Audigy 2 6.1
Moniter:19" CRT moniter capable of 150 Hz
Mouse: IntelliMouse Explorer USB 3.0

Is this system good what i indeed to use it for? Has anyone else had any experience with a sytem of similar specs? Would i be better to spend an extra couple of hundred pounds and get and Athlon 64 instead? Should i wait and the get the next gen graphics cards before buying?

What are your opinions?