Your motherboard memory and your graphics card memory can be different DDR types.
In fact, the graphics card won't use the the motherboard DDR memory even if both are the same type.
They don't and shouldn't interfere with each other.
The only situation where the memory is shared is if you are using onboard built-in graphics. In this case, you can set the memory allocation in BIOS for the onboard graphics.
Thank you for your response so quickly dragonic. Much appreciated help!! I have googled the question and thought that just joining a site, as this one, would be my better bet. Thanks for making my first experience, here, a good one!! Cheers!