I've got this responsive email template (that's just a portion of it, more on jsfiddle):
<!--[if mso]>
<v:roundrect xmlns:v="urn:schemas-microsoft-com:vml" xmlns:w="urn:schemas-microsoft-com:office:word" href="http://byensejendom.dk/conference/signup/559"
style="height:200px;v-text-anchor:middle;width:140px" stroke="f" fillcolor="#9B4242">
<w:anchorlock/>
<center style="color:#ffffff;font-size:16px;font-weight:bold">Tilmeld dig</center>
</v:roundrect>
<![endif]-->
http://jsfiddle.net/cC5tr/
Here are results from Litmus: https://litmus.com/pub/74df5e9/screenshots
The section that SHOULD format the button right next to the image is enclosed with tags, however I can't get it right in 2007,2010 and 2013.
Thanks