I have a PC with an ASUS P6T SE motherboard and an i7 920 processor. I noticed that the machine came with some software called "Turbo V" which appears to allow overclocking - but I can not find any manual for the software. Does anyone know how to use this software? Or where a manual is?
The user manual that came with your ASUS motherboard should have a section with information regarding the usage of Turbo V. At least my ASUS board did, though it was a different model. Regardless, Turbo V is indeed a motherboard overclocking utility for ASUS motherboards.
There are two pretty good sources of info regarding it's usage. The first is the ASUS website. If you go to support, search both in the motherboards section for downloads for your specific model. You should also check their forums.
The other source you should check out is YouTube. There are some pretty good videos created by other users on how they are using Turbo V with their boards.