First, compile and install libdvdread and libdvdcss. Use google or something to find these parts, which are available from various different places.
After installing those parts, before compiling MPlayer, do a "configure --disable-mpdvdkit", which apparently avoids the mpdvdkit, and makes it use the dvdread and dvdcss libraries, if found.
Then, run "mplayer " to view the dvd.
Chances are that dvd:// doesn't work, which might be because your system doesn't have the /dev/dvd setup. It's probably a good idea to create a symbolic link from /dev/cdrom to /dev/dvd to fix it.