Hi Tanya

You can either do this in two ways:
1) via a post-processing macro, which you run over the
doc once you're finished; or

2) I'd suggest you try using the AutoCorrect feature in
Word (Tools>Auto Correct). Enable the box "Replace text
as you type" and add an entry for a full stop. In
the "replace with" section put the full stop and two
spaces. Now everytime you hit the full stop you'll get a
full stop with two spaces.

Hope that's been of some help,
Dennis