mplayer will work like a charm. i'd not be too sure that the machine is fast enough to ever deal with DVD. but if it is, then MPlayer will be able to play it.
however mplayer isn't supporting functional dvd navigation though. so you'd need to select the track and such. you also are after auto insert notification, which i don't think is really used under linux, not heard of it myself...
if you just want the dvd to start playing the main filjm instantly you would need to find out the main title anyway, and actually thinking about it dvd navigation is presuambly something you wouldn't want. i have written a program called lsdvd
http://acidrip.sf.net/lsdvd.html which you could use to find what's on the dvd. from there you'd need to work out which is the longest track and then use mplayer to play it. if this sounds scary i quite like the idea of modifying myprogram to tell this automatically.... so i'd add that functionality in some form or other just for situations such as this.
BUT you've still then got the automatic notification... and i know nothing about that.... but mplayer is certainly the way forward i'd say, just as long as it's easy enough to pass the right inoformation to it.
hmm, don't know where i got the impression it as for kids... but i never mentioned that out loud did i? odd....