I is now really easy to run DIVA-GIS on a Mac (OSX) with an Intel chip. This is because Mike Kronenberg has added DIVA to the the "predefined prefixes" in winebottler. Many thanks Mike! Also thanks to Jonathan Fresnedo for instigating this, and for showing me the result.
First download, install, and open winebottler. Then click on DIVA-GIS (under the predefined prefixes menu). That's it!
If you do not want to use the predefined prefix (or if you wanted to install a different version of then the one available in winebottler), this is how Mike set it up:
1. open WineBottler
2. select the "Create custom prefix" from the sourcelist
3. in the "Installer" section, find setup.exe