Ok ok ok wait......Never ever in my entire life has a teacher (especially IT ) required us to go online and ask questions to random forums.........
You need to figure this out on your own. Its the only way to learn it.
If you had bothered to do a google search for dcom vulnerability 3rd hit is this"http://www.sans.org/reading_room/whitepapers/threats/examining-rpc-dcom-vulnerability-developing-vulnerability-exploit-cycle_1220
Very detailed paper on all of the questions you are asking. I saved you 30 seconds!