This isn't really a "graphic design" answer, but you may also want to see if you can change the text. In your examples, I don't think the art of the "install" button is particularly more button-like than your Outlook button. However, the text on it is a well-known verb so it is associated with performing an action. In the same vein, "Launch Outlook" may attract more clicks than simply "Outlook".
From a graphics standpoint, (and further to jhocking & luckycypher's comments), some other things you could try:
- Make the edges glow on hover
- change background/border color schemes on hover
- add a subtle shadow (with or without beveling the surface) so the button appears raised from the page
- add a small icon next to the text to indicate what action is to be performed (if I 'Outlook', what am I doing?)
- place your button in a location where other buttons are typically placed on your site
- make the button theme match other navigation links/buttons on the site.
You could also try asking over on UX for other UI-centric thoughts.