There will be some major changes to Outlook 2007 Microsoft that you need to be aware of - the most important being the way Outlook 2007 will render HTML emails. In previous versions Outlook used Internet Explorer to render HTML emails, but Outlook 2007 Microsoft Word will be used to render HTML images. In short, what this means is that no background images will be allowed (in div and table cells), no support for float or position which means CSS is a no-go (tables only) and even then there is poor support for padding and margins. Don't give up on your email marketing campaigns just yet though, you can download a tool from Microsoft that will help you in validating your HTML for Outlook 2007.