There's no way around it, html emails can render funny. There are so many variables. However, I think the trade off is worth it. The majority of users will see it pretty close as to how you intended it. The rest will have differing levels of glitches depending on their image and CSS support. If you stick to old fashioned tables and embedded font tags it seems to increase the chances of it rendering properly from my experience. However, even if it comes out all wrong your text and hyperlinks will still be displayed so at least they can read and do something.

You can also prove text only versions with the HTML version as well.