login.htm is a virtual URI. You won't find a file with that name.
Likely what happened is that Mango failed to start for some reason. Check that there is a <tomcat>/webapps/mango directory. Also, check your <tomcat>/logs/localhost.<date>.log file for error messages.
Thanks for your quick reply. It turns out I did miss a step. I had tomcat 5 installed and I assumed(wrongly) I could get away without upgrading. I will try again after a settle this issue.