Switching voices in the speech SDK

PLEASE HELP! I've asked this question on the Excel programming group,
they're usually very knowledgeable and helpful,but everyone always
ignores this one! maybe nobody knows the answer.

I want to use the speech facility in MS Office to read out cells from
Excel - within a VBA to tool I'm using. It works fine, but I need to
ensure that the right voice is used.

I can change it in the control panel, but I need to do it in code...

Does anyone know the code or API or whatever to make it switch to a
particular voice e.g. "Microsoft Sam" or "Michelle" I really hope
someone can help..

Thanks, Michelle