The controller chip in the B&W has been holding up dual-processor upgrades. Sonnet has found a way around it and should be releasing dp upgrades shortly, say a month or so. At least this is what they said.
The B&W is the sweet spot in PowerMacs to upgrade IMHO because it's the first PowerMac with a 100MHz system bus. The beige Macs had 66MHz buses and slower. The only problem with the B&W is lack of AGP graphics - Quartz Extreme in Jaguar can only be implemented with a hack, and you'll only get a little, if any, of the benefit.
Keep checking their site:
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