@wac. I'd just doit in plain HTML tables, if you start to add CSS you'll start and discover compatibility issues. Draw out the template on paper and slice it up first and add notes, it'll make life easier.
However, this is quite a tricky mailer to be honest. You have overlapping elements which tables cannot really achieve. It depends which areas need to be clickable.
Also be aware of the "click here" having click here will effect your spam score big time. I'd probably keep that as an image and just have it clickable.
I know your not using this service but have a look at how a few mailchimp templates are created, and be sure to check out http://kb.mailchimp.com/article/how-spam-filters-think