The upcoming Silverthorne CPU seems to have been divided into several SKUs with different thermal envelopes: the SV or standard Voltage, the MV or Mid/Medium Voltage and the LV or low Voltage versions.
The SV edition will aparently clock as high as 1.86GHz and starts at 1.33GHz and operates on a 533MHz FSB with a TDP of 2W. The MV edition is slower at 1-1.1GHz, it uses a 400MHz and has a TDP of 1W.
Finally, the LV edition will be clocked at between 600 and 900MHz, again on a 400MHz bus and with a TDP of a mere 0.6W. It is also rumoured that Silverthorne will feature HyperThreading, which makes sense, as this could potentially make better use of unused CPU cycles.
It will also support SSE3, XD bit and VT technology and, interestingly enough, IA64.