You have VLC right? Open it, then click file, then click on open disk. Select the type as VCD and give the path to CD (hdb,hdc whatever).
If you can mount the CD, then this method works. As far as directly playing dat files that are not in a VCD structure, VLC does that too. (ie :- you can play them as well).
(I have not tested this method on Ubuntu, but it works in SuSE, and it should work in Ubuntu also)(Should, not will).
Aditya