I am now entering a stage where I feel confident enough to over clock my pc( after much research).
I currently have a HP A6090.uk Intel core duo E6700 running at 2.66Ghz with 3gig of ram. I have a changed the power supply to 700 watt and dumped a XFX geforce 8800gt xxx apha dog to play with.
I haven't changed any of the fans as the cpu never get above 50 under load and the gpu never goes above 70.
The system is very stable but what I would like to know is what speed would people recommand ( I have seen them running at 3.5 and above) with the current cooling system or should I upgrade the cooling system? then over clock?

Any thoughts?

Yes get an aftermarket CPU cooler. Keep in mind that you will have to clean off the old thermal paste and apply new clean thermal paste when you change the cooler. Overclocking is increased little by little until the computer won't start. Make note of the overclocking values and when the computer won't boot, use the last working setting after you reset the CMOS and get the computer booting once more

Thanks, is there any cpu cooler you would recommend? is the temp really going to be going up that much?

You would be surprized on how much the CPU temp goes up. My Q6600 running at 2.55GHz OC (Stock 2.4GHz) went from 43C to 55C. I use a ZeroTherm Nirvana. Check out ZeroTherm for a socket 775 cooler

3.66Ghz should be the maximum stable overclocking speed for E6700.

You can try out some 120mm fan heatsinks, Thermalright, Zerotherm etc..

I use a Thermaltake V1, and can OC my Q9450 to 3.5Ghz stable, at like 57-59c Full load (Prime 95 for 20mins straight toruture test)