How do I add display ads into my newsletter?

Hey-

We run a small B2B media company and use Constant Contact for our subscriber eNewsletters.  I'm looking for a better solution to add display ads into our eNewsletters (we use Ad Butler for our website).  My challenge is that currently we have to do this manually and reporting is a nightmare.  I'd like to incorporate the Ad Butler codes into my newsletter but it says we need a custom coded newsletter template and not sure how to do that.

Any suggestions?