A good mother board, with decent overclocking features is Asus P5N-D sli ( ASUS - Motherboards- ASUS P5N-D
or Newegg.com - ASUS P5N-D LGA 775 NVIDIA nForce 750i SLI ATX Intel Motherboard
) -Just like mine
Offers you a 20% OC, has 2 PCI-e slots, ATX format, 775 (supports quad core processors), 4 DDR2 800 slots... pretty good
Not sure for the price,or is it even "buy-able" anymore... But if you find it, i think it will be good for your needs.
As for the DDR2 and DDR3, i strongly suggest you to buy DDR3 board because it is much more cheaper, and you have faster modules - 1600mhz; 1333... In my shops, for an average quality brand, 2 Gb DDR2 @ 1066 cost the same as 4 Gb DDR3 @ 1333.