I found some more information on the Internet, but for AMD. I wonder if I can get any info from it. Unfortunately, the site is currently down:
http://kat.student.utwente.nl/~matthijs/cgi-bin/blosxom/Hardware/S270/Undervolting.html
Also, I wonder whether I can just set the CPU frequency under FreeBSD or Linux and read out the voltage in order to create a table for the time being...
Still, FreeBSD uses this ACPI throttling thing, which I should port sooner or later, since Intel stopped releasing CPU frequency/voltage specs...