For now no m-ATX mobo with SLI or Crossfire exists for Core 2 Duo. Most boards use the G965 chip. It is a real, real dog when it comes to overclocking.
The only m-ATX mobo for C2D which allows you to OC (that I know of) is the ABIT IP-95 LGA 775 VIA P4M890 Micro ATX. According to one user review, he was able to OC the E6600 to 3.4GHz.http://www.newegg.com/Product/Product.asp?Item=N82E16813127017
I'm kinda eyeing this mobo for my next HTPC.