For the $200 range, P4 is totally out of the question. You need to get Athlon or Athlon XP.
Go here. You want one of the "Athlon (OEM) & DDR Bundles".
Get a motherboard with VIA KT266A or VIA KT333 or nVidia nForce chipset, at least 256 MB of RAM, and as much CPU as you can afford.
If you are wondering what chipset a motherboard has, just
go here and look up the manufacturer and board and click on "specs".
I have had a lot of good luck with Epox motherboards.
PS If you get VIA KT333 you will want PC2700 RAM. You can get bundles with that RAM
here.