both xeon and p4 will have a newer version with 2mb of cache soon. (perhaps first quarter of next year) it should give some performance boost on the prescott core.

Dual cpu system is better in multi-tasking. you can encode dvd, using internet, burn cds.... at the same time. if that's how you are going to use the computer, 2 cpu is better than one. however, if you are going to use it to play games.. most games don't run any faster with the additional cpu.