You need to increase the various subsystems gradually and test at each stage to find out where and what the limitation is (ie FSB, ram, or cpu's capability). There are many good oc guides out there, including these forums (check out many q6600 threads). Out of interest what are the bios setting you are using/are available?
q6600's are power hungry and the board is a G41 with fewer power circuits than more expensive models with overclocking in mind, so a high oc might be detrimental to your boards health in the longterm. Additionally the fewer power phases mean it wont be as capable at provinding stable power at higher voltages/power draw especially as they heat up due to increase draw.
A 3ghz oc might be reasonable with speedstep enabled and some cooling on the mosfets however. No guarantees though.
