Hardware combination?

HP

Hi. I have a dual processor P4 2X3GHz, 2.5 GHz RAM (windows xp) and I was wondering what is the best (I mean faster!):

1)Buy one more dual processor e.g. P4 2X3.6GHz and have them (4 CPUs) work in parallel? (of course the second dual cpu PC will be using windows 32 to match the first). This case is not considered very expensive.

2)Buy one dual processor 64bit machine with linux (and fluent 64bit) and have it work alone (2 CPUs in parallel without the first dual Pentium 4)

3)Any other solution more or less with price on the same order of magnitude with the other two (or more expensive in the case that perfomance is much more increased relatively to the price)

Thanks in advance for your help.