Was running into this problem. TFS 2010 with MOSS 2010. Whenever i browsed to the process guidance or any html pages in the portal, i would get a prompt to save dialog. Turns out, this is a change in MOSS and their default security settings.
in a nutshell, open sharepoint central admin, switch to web applications tab, then open general settings for the site you want to change, go to Browse File handling settings, change the setting from strict to permissive.