You can read how to install a mud pan shower base in books, but I personally would leave this job to the pros. Must support the weight of the mud pan. Must protect from moisture and leaks. This is a job you don't want to have to redo. It would be massively expensive to redo.
Good luck. Make sure you know plenty before you begin.
There are sites that give home remodeling tips such as this one http://www.housenet.com/iq.asp?CategoryID=102&SubCatID=1&Sub_CategoryID=1&Detail_CategoryID=110&ArticleID=0