http://support.microsoft.com/kb/937160

Description of Visio Viewer 2007 Service Pack 1

At the moment, Microsoft have released this as a Service Pack only. If you try to run this without having the original Visio Viewer 2007 installed, then you will receive the following error:

There are no products affected by this package installed on this system.

Hopefully Microsoft will re-release this as a standalone installer.. doesn't make sense to have to download a 9.62MB Service Pack when the original installer was only 7.69MB.