(I've moved this over to the Content Manager's forum for general interest)
Hi David,
If the emails are going to be sent from Outlook, then the Outlook templating system is the way to go.
View this video for an excellent overview on how to obtain and modify ready-made Outlook templates from Office Online, followed by an example of how to create one and save it. Make sure you watch it all the way through as it touches on more than one subject.
The templates are made in HTML and you can use an external editor if you want, but it is probably easier to use the editing facilities in Word, which is normally the default editor in Outlook. Note that the default editor can be changed, so if it doesn't look like Word then it probably isn't and should be changed back to Word in the Outlook preferences.
It's worth viewing test emails in different email applications, and at services like Hotmail, Gmail and Yahoo so that you can ensure it holds together. It is if course best to keep templates simple.
That should get you moving in the right direction.
Rob
(video link updated)