By default Totem can't play VCD/DVD etc., But by installing the plugins it can play.
You need to install Restricted Formats like Windows Codecs, etc., See the below
URL:
*wiki.ubuntu.com/RestrictedFormats
Regarding your second question. When you insert a VCD , Totem loads,terminate
it (File->Quit). Go the VCD folder where the '.dat' files are stored and select
one file , right click 'Open with Other Application' Now it will open a dialog box
containing all the applications. Select VLC Media Player in the list. Click on 'Open'.