t-i-m-m-y, one of those video cards alone would cost 700 bucks. Please think realistically. That's half the cost of her goddamned machine!
Look, fantasia, even a Radeon 9600XT could handle Doom 3 very well. And guess what? It's 1/3 of the price of those high end useless gfx cards with a ton of frills.
I'd say 1 gig of ram is pretty good, just grab a Geil dual channel twin stick combo from fluidtek for 275 (2x512mb, 400mhz). Having low latency is great, but you seriously cannot tell the difference when you're doing stuff on the computer. Seeing numbers and stats is one thing, but feeling the performance increase is another. If you're going to blow $50 just so that your ram has 1 less latency on all aspects, don't bother.
Don't believe the hype of DDR2, or 533mhz ram. It's just plain stupid. You don't need the BLEEDING EDGE of computers. People with $3000 lying on the floor can spend a shitload of money on those expensive components. I'm sick of people recommending other people fancy schmancy stuff at high prices. It's like buying a top rig costing their life savings, only to waste it on checking email and chatting.
Basically fantasia, you don't need to buy one of those really really expensive video cards. Unless you have money of course.
If you have a look at the benchmarking for both the P4 and AMD64 speeds, the AMD systems are generally faster at gaming. It is recommended to get an AMD, as they are currently crushing Intel
For gaming, most of the tests don't even bother with the speeds of the CPUs. It all comes down to what video card they're using, but yeah, I'm getting an AMD one. As azn_boy said, there's a good CPU/Motherboard set at centrecom.com.au, AMD Athlon 64 3200+ (S939) $257.40 and Asus A8V Deluxe (VIA K8T800Pro/939) $212.30 . That's an exceptionally good price. Great motherboard too... just a bit ugly =/
Getting a socket 939 board is better because that's where AMD's future CPU lines lie. It will grow further in its series, so if you don't feel you are getting enough in a few years, AMD will have plenty of sk939 CPUs for you to buy
Getting a top gaming/DVD/music soundcard is not really important. If she wants to spend $165 on an Audigy 2 ZS just to experience Advanced EAX HD in games, then fine. Onboard sound is enough these days to compete with PCI soundcards. It's quite scary. I'm assuming onboard can go up to EAX 2. Which is still very good (considering I don't even know what mine is which=no EAX)
Get a roomy hard drive. They're dirt cheap. My advice, customise your own system. If you're lucky, you might find a nice case too.