As far as I understand, you have an Intel(R) Desktop Board DG35EC with a memory configuration question. If my inference is correct, I confirm this board model in question does support DDR2 800 and 667 Mhz. SDRAM; see the following URL:
Just know that if you mix the memory frequencies, the system will downclock the module with 800MHz. to 667MHz. to match the slower module. For further memory configuration details, please, refer to pages 17 and 18 of the Technical Product Specification:
Gracias me sirvio y sirve de mucho.