you can get the same performance by overclocking the cpu. the multipliers are ways of upping the FSB of the cpu. in changing them you can make the cpu run faster than it is rated at
I would suggest that you upgrade your mobo and get a good dual core CPU. You can get a decent dual core intel processor (2 x 2.2ghz or thereabouts) for around £60-£70. as for the motherboard you should be able to get a compatible one for around £50. Its definitely worth getting a good CPU as I recently found when hopping from a shocking 2ghz to 2 x 2.66ghz
How exactly would I get the same performance as a 6400 with the 5000? What is a good (not too expensive) motherboard that would go nicely with the CPU and would my ram be compatible with it? Sorry I know I'm a huge noob.
x2 6400+ and 5000+ BE both come with Unlocked Multipliers
Getting to 3.2GHz with the AMD Athlon 64 X2 5000+ Black Edition is stinking easy. No need to do anything except change the multiplier to 16 you have a X2 6400+ without the issues of a Windsor Core!!