I was working a project schedule with MS project. I started by estimate the duration in 'months' using PERT, and later I decided to switch to 'days'. The I run into the duration format convertion trouble. I fund the set the 'Duration is entered in' drop down list in option menu didn't really do the job. See the full solution:
geekswithblogs.net/chrishan/archive/2008/07/18/123879.aspx