$200 doesn't give you much to work with. Any new MB and CPU are also going to require you to get new ram (DDR most likely) and probably a larger power supply than what you have.
That said:
If you go AMD, you want an nForce 2 based board. IMO no exceptions. The VIA KT400 chipset is the closest competitor, but can't match the speed nor the stability of the nForce 2. I prefer the Asus A7N8X (there is a Deluxe and non-Deluxe version, the Deluxe version has just about all one could dream of but onboard video).
The non deluxe version of this board will probably cost around $130 and the Deluxe about $160.
Currently the AMD CPUs at 2200+ and below are very well priced. A 2000+ is probably the best bargain among them. CPU prices are going to vary A LOT depending on who you buy from.
If you go Intel I prefer the 845PE chipset based boards or the new Granite Bay chipset. (I haven't personally tried the latter though...)
Intel P4 CPUs are significantly more expensive than AMD Athlon XPs at the 2.2 GHz level and below. Unfortunately, they also do not outperform the equivilant AMD products either IMO. If you go Intel the best bang for the buck is probably a 2.53 GHz 'B' model, but that will cost quite a bit. It's only the 533 MHz FSB 'B' type P4s that are even worth considering IMO.