where can i find a technical description of how bitlocker works?

Mitch Tulloch posted a short article looking at both the business imperitive for securing corporate laptops and technical basis for doing so with Bitlocker on Windows Vista.

Mitch's post includes links to some interesting sources of information including the Microsoft TechNet "BitLocker Drive Encryption: Technical overview" which is well worth a read.

Beware that some high level details have changed since the overview was written.