Optimal...I guess I'll give my home PC as an example. I play at 1920x1200 with all settings maxed.
Intel Core 2 Duo @ 3GHz 
4GB System RAM 
GeForce 8800 GTX 768MB PCI-E Video Card 
SoundBlaster X-Fi Fata1ity
I run it on Vista 64-bit, but if you have anything even remotely close to the above system on XP, it should be more than enough. 
nice...  

 and when I can make a 6 digit annual salary playing computer games I'll have a system like that..  

, 
until then my real career (which does make me 6 digits  

 ) demands I travel frequently and therefore a desktop or even one of those silly gaming desktop replacements pretending to be a laptop arn't very useful 
what I got comming sounds like it should be just fine or at least pretty close to it, especially since I'll be playing on a much smaller screen. (1680x1050)  
Athalon 64-T66 - 2.3 Gz, 
4 Gig Ram, with the
512Mb Raedon HD2600 (yea I'm well aware it's really 256 mb)
64bit Vista...  
 a 8800GTX video card would have been nice but when your running laptops heat and battery power are a small consideration... 

, any bigger than a HD 2600 or 8600GT your cooling requirements are just too combersome. The 8600GT was what I wanted but it pushed the price above my budget ceiling, (amazing how quickly 3 kids will eat up an afore mentioned 6 digit salary 

 ) the chipsets aren't quite as adaptable as in a desktop so I was stuck with the AMD chipset... (I did find a Core Duo with the right chipset at the right price but not until last night after my AMD based machine had been shipped  

 but I couldnt get it with 4 GB Ram or 64bit Vista, so I'll stick with what I got ) 
I did look at a Gateway midrange laptop with the 8800GTX card for like $1350 but some accountant calling himself a computer designer paired it with a core-duo 1.6 Gz chipset.... have to say it's the first time I've seen a configuration where the processor is the bottleneck...  

  - only reason I can think is they wanted to keep some semplence of battery life and so scaled back the processor.