I have both a VIA KT400-based board, and an nForce2 board. The nForce2 is leaps and bounds ahead of the VIA chipset. Definitely spend your money on the nForce2 board. My suggestion is the Asus A7N8X Deluxe. It's got bells and whistles you'll probably never use, but it is solid as a rock.
The graphics card debates will rage on forever. One company or another will be releasing a new product every couple months to try and stay ahead of the curve. Current top of the line chipsets are the Ti4600 from nVidia, and the 9700 Pro from ATI. As was mentioned previously, the ATI card may be a better buy, simply because it supports DirectX 9. However, look at the software you're playing on a regular basis. Currently there are no games that utilize the features of DirectX 9. The Ti4600 will save you a buck or two over the 9700 Pro. As for manufacturers, Leadtek is my recommendation.
For an AMD system, I'd spend the extra money and go with one of the new Thoroughbred-B chips on the 333MHz FSB. This will offer significant advantages over the older Thoroughbred-A core. Not only is it better in heat dissipation (larger die size) but the extra horsepower on the front side bus helps you tweak out the most from your AMD chip.
Memory is another area to consider. With the nForce2 boards, you can utilize dual channel features. Definitely buy good memory. Mushkin and Corsair XMS get my top picks. Go with 2x256 sticks of either PC2700, or if you want the PC3200. The PC3200 doesn't offer too much of an advantage over the 2700, so if you want to save a couple bucks, stick with the 2700.
Approximate prices listed below:
Asus A7N8X Deluxe -- $126
AMD Athlon 2600+/333 MHz FSB -- $275
2x256 Meg Corsair XMS PC2700 -- $200
Leadtek A250 Ultra Ti4600 -- $240
A couple more things to consider with these components are:
1) Get a good cooling solution. Something that is either pure copper, or a copper insert into an aluminum sink. Swiftech makes great stuff. Along with this, get a good fan. Something that won't make your PC sound like an ME262 spooling up...
2) Thermal grease. Invest the 10 bucks in some Arctic Silver III.
3) Power supply. Make sure you've got at least a 300 watt supply from a trusted name. I'd suggest getting an Antec 400 Watt True Power supply (although it will set you back about $100). The 300 Watt version should cost about 60-70.
Hope some of this helps.