Wing Commander CIC

I had to enable compatability to load up the first disk with I, II and III for K Saga..but..i am wondering what the other four disks are for? It said it installed I, II and III from just the first disk. Can anyone explain how it works? thanks

IV would not install yet, i will try compat....but wanted to ask about the disks first.

thanks

and are there upgraded movies or other patches to add ?

I have Windows XP SP 3 Pro running with an FX 9600 Card...