Here is a good guide to overclocking Intel processors. It is long but extremely thorough.
HOWTO: Overclock C2Q (Quads) and C2D (Duals) - Guide v1.6.1
You motherboard is based on the 945G chipset which is not known for being good at overclocking. If you want to upgrade the Abit IP35p is based of of the much newer P35 chipset which is an excellent overclocker.
Newegg.com - ABIT IP35P LGA 775 Intel P35 ATX Intel Motherboard - Intel Motherboards
What would be a good new motherboard?