The MB does support 1333MHZ but it is OC the RAM, here I copy from MSI:
Intel® G41-based motherboard
- Supports FSB 800/1066/1333 MHz
- Supports two DIMM DDR3 800/1066/1333*(OC) DRAM
- 4 SATAII ports and 4 rear USB 2.0 ports
- 7.1 channel audio output
So if there is not option in the BIOS to change the voltage, you need to play with FSb, Cpu Speed, FSB RAM ratio speed a lot more, otherwise just use the 1066MHz, because we don't have the real same PC we can't give you exactly step by step instruction. Sorry abut this.