Just a couple other thoughts on your current setup (and no I wont tell you to buy a new one lol, although thats really what you need).
Your video drivers are way out of date. Like probably a year and a half to 2 years old. Still, if you can get into the game and make it work, the old saying goes "if it aint broke, dont fix it." I dont know how you get in, as I didnt know they ever made a GeForce2 card that would be Dx 9.0 compatible. But maybe if you dont tell it that its not supposed to work, it will keep going.
The onboard sound is probably eating up CPU time. If I were you I'd seriously consider finding a cheap soundcard somewhere. The low end SB cards are not expensive, and most computer stores sell even cheaper knockoffs of the SB cards. Just make sure you download the newest drivers from the company's website, and I'd turn down the "hardware acceleration" on the sound to 3/4 or 1/2.
Most important (from my POV) is, if you can, upgrading that CPU to at least an 850 or 900mhz. At least you will be within the minimum specs and can be more sure its not a CPU problem when you crash. AHII is very CPU dependant, and the better CPU you have, the better the game will perform. You should be able to find one of these fairly cheap.
Finally, if the 512MB issue is fixed for you at this point, (IMHO) you should seriously consider finding another 512MB stick and bumping your system up to 1 gig. Preload textures to memory, to help save some CPU and VPU lag and "stutters". Regardless of the age of your video card, with only 64MB of memory it is going to be hitting your processor all the time to help it out. Having the extra memory so that you can preload some of it will help. Having the newer drivers would probably help some more (although I'd make sure I have the old ones ready to reinstall if you have trouble).
Again, just my opinions. If your setup works as it is, ignore me. Playing around with it might just put you over the edge into unplayability. But if you are having problems getting in, maybe this will help.