You have two primary issues

In order to save money, ASRock have selected the i945 chipset, which was not originally designed to support Core 2 processors. While it is technically possible to get Core 2 support due to the i945's Pentium Extreme Edition support of 1066 MHz FSB (1333 Mhz was never supported so forget about it), the biggest limitation is the power design. Since AsRock motherboards have very cheap power circuit designs, support of new Core 2 processors as they're released is not guaranteed. Furthermore, if they don't add BIOS support, you might be faced with a no-boot situation.

Your second issue is, even if you could get a Core 2 Duo E6750 to run at 1066 MHz FSB0, due to the core ratio of 8, what you'd have on your hands is a Core 2 Duo E6400.