Write it like a webpage and point all the images to where you have uploaded them to the internet.
Be careful with css in html emails. It's doesn't work as well as in regular web browsers.
If you are using an email client like Outlook or Thunderbird, they have options where you can either write WYSIWYG emails, or veiw the source of the email and paste the code for your html email. Test it in as many email inboxes as you can, send it to your friends first and have them check it in gmail, hotmail, yahoo, etc.
