Emails can be formatted in whatever format you deem to be the best for what you are trying to convey. However, due to the complexities of using an XHTML based email I would highly suggest you hire someone to code the email for you if you do decide to use an html format.
The person who codes your email should also have experience in building table based email templates that render correctly in Outlook 2007 along with Gmail.
If you are looking for a quick and easy formatting solution I would suggest going with one of the well known ESP (Email Service Providers) such as Constant Contact.
If you do decide to use a text formatted email you can definitely do the writing and basic styling. Plain text emails also degrade nicely if you have someone using very old software.
Hope this helps ;)