Pollock, what's the problems you are having with the existing system? Those A7V series boards can be tricky to setup, but I've always managed to get them rock solid stable. (The newest VIA drivers modify some AGP timing on the KT133a boards like yours and really do seem to help in stability. The only problem is best results are obtained if they are installed right after Windows.)
Is the nForce a stable board? From firsthand experience and from reviews I've been reading; I'd say yes. It is still very new though, so issues may pop up. As you already know, it's not an overclocking board. Integrated sound, to put it mildly, is absolutely incredible. The layout of the board (at least the MSI K7N420 Pro I used) was the best I've seen in a long time.
I have a firm set of 4 rules when doing AMD Athlon based systems, if you break them you are asking for trouble:
Rule 1: 300W or greater AMD Approved power supply.
Rule 2: Top quality ram. (Crucial is good.)
Rule 3: Adequate cooling - this means an AMD approved (for the speed CPU you will be using) heatsink and fan. When you get the heatsink and fan, if it has one of those little square thermal pads on the bottom, scrape it off with a credit card and rag and replace it with some Artic Silver 2 (or Silicone heatsink grease). Those thermal pads don't work as well and they glue themselves to the CPU die, making getting the heatsink off in the future hard to do. The case must also have either (or better yet both) a spot for a rear case fan or a side panel mounted fan.
Rule 4: When building a VIA chipset based board, load the VIA drivers right after Windows. (Does not apply to nForce board, just use the driver that comes on the CD right after Windows comes up for the first time.) Violating this rule with a VIA chipset board will ALWAYS result in an unstable (in games at least) system if you load the video card drivers or Direct X before getting those VIA drivers in.
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Pollock, if you do want to do a system with this board, private message me. The manual it comes with is pretty sparse and I can save you some trouble setting up the board. (For example, the locations of the pins to plug on the power switch connector.)