The first thing you wonna do when OC'ing on an ASUS MB is to disable all the energi saving/auto OC'ing functions in the BIOS.
That'll, for the P6T deluxe V2, be the Enhanced Intel SpeedStep (found in the AI tweek section of the BIOS)
And also the Enhanced Halt State aka. 'C1E' (found in the power section of the BIOS, if i remember correctly)
As a start, you could go with 20x140Mhz(BLCK) which will bring your i7 920 to 2.8Ghz (~5% OC). For this you can keep all voltage settings at auto.
Make sure your ram doesn't exceed the 1333Mhz (their rated speed) even if it means dropping them ~100Mhz. It'll decrease your memory bandwidth a tiny bit, but it's safer.
This is normaly done by setting a FSB/DRAM ratio, but on the P6T D V2 it's done by choosing the DRAM frequency corresponding to a sertain ratio.
Go for the on closest, but under the 1333Mhz marker for starters.
If you wonna up it more, increase the BLCK with a small increment (I like to start at a round number, hence the '140', and then increaseing by 2Mhz BLCK).
Keep monitoring your temps at both idle and load. (I would say keep it a couple degrees under 80Â°C hard load) - I use CoreDamage, let it run for at least 15min to get an idea about how high the temps will get.
When you get to the state where the CPU gets unstable (non POST'ings or crashes/BSOD's in windows), set the vCore voltage manually to the rated voltage (think it's 1.2v or 1.25 for the i7 - but check first). If that doesn't stabalize the system, up the voltage a tiny bit(1 step increments), or lower the BLCK by 1Mhz decrements till stable.
Once you've found a stable CPU OC, you can try going over the 1333Mhz Mem frequency.
Same thing goes here, as with the CPU, for unstablility. ->BUT!<- Never exceed 1.65v as i understand it can damage the CPU.
Anyways - OC'ing is an art, there are so many ways to it. Eventually you'll probably find your own way, but untill that i hope this has been helpfull.
Good luck dude, and happy OC'ing!