The G41 chipset is no good for overclocking (I personally wouldn't attempt it because it can provide nothing but headaches). To make matters worse, ASRock's 775 motherboards were not good for overclocking at all. On top of all that, Micro ATX boards for socket 775 were generally not good for overclocking either. So I think it would be better to not attempt it.
If you're in doubt about my advice, then I recommend asking for help over on Overclock.net
. One thing you'll be told is that your best bet is to find a motherboard that has either the P35 or P45 chipset. The P45 chipset is noticeably better for overclocking.