Ok, Westy... Check it out.. Not to knock all these guys, but I doubt most (if any) of them even looked up your mother board to see what it'd support...
You can make this system play AH very well.. But it may cost you a little.. You'll have to be smart about it.. Stick with 2nd hand stuff because anything you get new in the package is going to be outrageously over priced.. You can occasionally run into deals at places like Fry's Electronics if you have one near you.. But most places will rape you blind on older stuff from some stupid reason.. There are deals all over for older hardware, but you have to look.. Craigslist, Amazon,Ebay come to mind.. Some one recommended a processor... Yeah, don't get that P4.. You can find P4 3.2ghz HT 800FSB 1meg cache for 40 bucks or less.. The most your board will support is the P4 Extreme Edition 3.4ghz)the fastest Socket 478 processor produced).. Not much of a boost from the 3.2 I mentioned... Your board supports an 800mhz Front Side Bus, and is especially good at overclocking..
First off, you'll have to ditch the ram you have as it's holding you back.. You need some high performance PC4000 DDR 500 Dual Channel that will allow you to take advantage of the performance available.. IF you can't find any PC4000, you can use PC3200.. Just get something decent(Crucial Ballistix, OCZ, Geil, etc).. Right now, you're not even using Dual Channel mode with the two different kinds of memory in there.. You can find Kingston HyperX PC4000 or more brands all over eBay.. Get one gig (usually around 40 bucks or so). If you can swing 2 gigs, I'd advise that.. Anything more is a waste of money.. By the way, if you go with 2 gigs, you'll need two 1 gig sticks(or if you go with 1 gig, you need two 512's) to take advantage of Dual Channel mode.. I also would like to stress that it is better to have 2x1 gig as opposed to 4X512 sticks if you want a total of 2 gigs.. Your timings will be off and your board will actually clock the ram and your FSB slower than what it's rated at(ram buffer and memory management issues will arise using 4 sticks)..
The stuff is sold in pairs..
Third, you need a better video card.. Straight up.... Even if you got the fastest Socket 478 processor, it wouldn't make much difference.. That card is seriously holding you back.. You could do so much better.. If you like Nvida, stick with anything like a 6800GT/GS or a 7800GS/GT if you can find one.. You are obviously limited to AGP but you still have some very viable choices!
IF you want to go all out get the ATI/AMD HD 3850 which is (to date) the fastest AGP card available IIRC.. A power supply upgrade may be in order, though.. I would use something closer to 500 watts, atleast.. And a decent PSU at that..
If you are interested, please PM me and I will help you further.. I can attest to the performance potential of a properly set up Socket 478 machine.. I use one to play AH on occasion and runs the game just great with almost everything turned up all the way (besides shadows) at a resolution of 1280X1024(on an Nvidia 6800GS modded a bit for more performance)..