Rizinc is correct in saying it really does all depend on your system. Every system is different, even if you got all the exact pieces you have right now and built a 2nd computer with it, it still wouldn't necessarily perform the EXACT same, just how computers are. So we really can't sit here and say 'It'll hit 3GHz guaranteed' because that's just not possible.
Slowly increase your FSB by 3-5 MHz increments, also if you can't lock your AGP bus then you need to get another motherboard, because raising the FSB raises the AGP bus which also raises your PCI bus which are set at AGP:PCI 66:33MHz and they HAVE to stay at those speeds, too much further and you'll start frying AGP and PCI components including your hard drives..
If you don't have an AGP Bus lock then your only alternative is upping the multiplier, but realize when you change the multiplier you are making a HUGE jump in speed compared to raising the FSB by 3-5.
Just make sure you have cool temps, AGP Bus is locked, you have access to your VCore voltage and just bump up the FSB 3-5 MHz, save it, check for stability and repeat, if it crashes upon trying to get into windows, then up the Vcore for stability