MSN? :P
Yeah I'm like the only man on argo without an msn.. but let me try to re-write the paragraph :P
First thing is, desmond got assassin genes in his blood, that was said in the 1st story. He has been chosen by the scientists to be their model or whatever you wanna call it ( I dont remember why, Rusty will surely know

) At the start of the 2nd game you see in a cutscene that Lucy killed the other scientist who were going to kill you, so, she kills him and helps you escape from the lab to her and her friends lab.
Then you connect to the other animus and the 2nd game about ezio starts. ( the scientists were apart of the absterego industry ).
About the animus, the animus is a projector which renders genetic memories in three dimensions.
In Assassin's creed, the animus acts only as a machine and plot element, allowing desmond to play in through altair's memories the same way the player controls desmond himself.
In Assassin's Creed II, its use was expanded. The animus became an interface to a new world, including information about the historical locations, people, and time periods.
That basiclly explains what is the animus.
Now about the ancestors, there's not much to say realy, Just that altair and ezio are desmond's ancestors and that's how he got assasssin genes, obviously.
Hope it helped you, if not, ask and i'll try to answer it.
Finally it allowed me to post
Randy Marsh - Scoooore