I would like to use WinMerge as the default diff tool inside VS2008 from the solutions explorer in place of the \"Compare...\" context menu item. Is this possible? I\'m looking
Yep, it's possible!
See this link: http://whyiamright.wordpress.com/2008/01/18/changing-the-diffmerge-program-used-by-visual-studio/
Tools-> Options. In the tree, choose Source Control, then the plugin of your choice (VS team Foundation, Source Safe, etc).
Click the "Configure User Tools" button, click add, then specify the appropriate extension, operation, EXE, and arguments list.
This site: has the settings for many, including winmerge: http://blogs.msdn.com/jmanning/articles/535573.aspx
EDIT: You mentioned VSS: Check out the Winmerge manual here: http://winmerge.org/docs/manual/VersionControl.html. It says how to do it about 1/5th the way down the page.