Here is a very good resource detailing what works and what doesnt.
There are also a number of free templates available to download. Why not download some and look to see how they are built?
I sent HTML emails in outlook express a long time ago but from memory this email client is one of the few that have an edit source button. I used to do all my editing / building first then copy and paste my HTML straight into the source.
Info on how to locate the source button