MySQL performance increase from dual processor?

[wargod]

We're thinking of upgrading our linux database server (Redhat 7.3) which we run MySQL on to a dual processor system. It is currently running on a P4 1.6 ghz system with 512 mb memory and we find that the processor is constantly maxed out. We're wondering what kind of performance increase we'd get from updrading to a dual AMD XP SMP system. What kind of support does MySQL have for dual processors? If it's not going to be a substantial difference then we wont' bother. I've searched and found only very general information on this topic. If anyone can shed some light on thsi for me or tell me their experiences with similar setups I'd appreciate it.