Problem with disabled VT
Some Core Duo era ThinkPad models ship with Intel CPUs that implement VT-x for hardware-supported virtualization, but the capability is disabled by the BIOS. The only known solution is to flash a newer version of the affected ThinkPad's BIOS.
See this LKML thread for more information.
For some reason, VT-x is disabled by the BIOS on some ThinkPad models. Before you attempt a firmware update, you should check this article to confirm that your BIOS version has VT-x as a configurable option.
Available BIOS updates
In response to the missing and also disabled VT-x option in the BIOS, Lenovo has released several BIOS updates for the affected ThinkPads to fix the problem.
Lenovo solved the problem with a BIOS update on June 6, 2007. Flashing the new BIOS adds a configurable option to the BIOS to enable or disable VT-x.