What is the second system ?
Anyway, first, I dont know if your bp6 can handle a 1Ghz CPU, and even if it does, save some money and buy a 866-933 Mhz.
Secondly, more than 256 Mb is overkill.. PC150 is no good unless you're into overclocking, and a p3-1000 is not exactly a great overclocker (nor is the 933 btw).
(btw, you have a SMP board.. why not take advantage of it by buying 2 cheaper CPU's ? Only if you intend to run W2K of course.)
Lastly, if you're into games, spend all the money i just saved you in a good videocard, like Geforce Pro, or Radeon DDR.