Just been reading the CF-Talk list and came across this from Jim Davis for Gmail
Just create a new folder someplace (I've only done this with personal
folders, but I see no reason that it wouldn't work with system folders as
well) and call it "Gmail". Then right click the folder and choose
"properties". Now select the "Home Page" tab. Check the "Show home page by
default for this folder" and enter http://gmail.google.com