First and foremost, before even touching the FSB you need to ensure that any variables that may get in the way of your overclock are held back so to speak. The main (and really the only one) is RAM. The frequency of memory is derived by the base front side bus speed of the CPU (266 in your case) and "multiplied". As it stands, your RAM is running at a 1:2 FSB: DRAM ratio, which means at 266MHz FSB, your RAM is operating at 533MHz. Remember, that you need to factor in "DDR" - Double Data Rate, which is where the effective frequency of 1066 (533 * 2) comes from. Now, the problem is that when you increase the FSB, the RAM will increase too and that'll hold you back. At a measly 300MHz FSB, your RAM will be operating at DDR2-1200, which it won't be able to do.
Anyway, the bottom line from what I've said is to set it to a lower multiplier/ratio such that it allows you to find your max CPU speed without the RAM getting in the way. Setting it such that your memory defaults to DDR2-667 at stock CPU speeds is your best bet.
Ensure that you've applied the correct RAM voltage and Timings for the memory as per the manufacturer spec.
NOW, comes the stage where you begin to overclock. Start at 270MHz on the CPU FSB, save settings and boot into windows. Use Prime95 v25.5 or later and run the
Small FFT's test for 3-5 minutes to see if it's stable or not. This is a very light way of confirming sufficient stability to move on further. Continue in 10MHz increments until Prime95 fails or the system freezes/reboots/bsod's. From this point, try increasing the Vcore in 0.01250V/0.02500V increments to see if it solves the problem. You'll get to a point where the tests are failing even at voltages upwards of 1.45V and at this point you know that you won't squeeze much more out of the CPU. At this stage you start backing down the overclock till it passes and you then move on to longer 4-8 hour runs of Prime95 to confirm 24/7 stability.
As for max temperatures for the Q6600, I would consider 70-75c as a safe max.
If you're still a bit unsure, have a look at a couple of guides and you should get the idea. My explanation is fairly short and only covers the crucial bits.