well the movie didn't take after any versions exactly it sorta took the characters and made a whole new plot like bobby and rogue were never together they sorta made they're own version the legacy virus is something i don't know much about it's a virus that was made to destroy all mutants on the face of the earth collosus (one of my fav. characters) gave his life to destroy the legacy virus. other people will know more about that.
An easy and probably inexpensive way of learning all about the X-Men is to go to your local comic shop and buy old issues of Classic X-Men which were reprints of the series starting at Giant Size X-Men #1. This introduces the recruiting of the new team of X-Men(wolverine, colossus, storm, etc) to go on a misson to rescue the original team. After that the numbering picks up where the original left off I belive issue #94. I say inexpensive because they are reprints and should have no collector value but are great for late comer fans. They also have stories in the second part of the book which were either new at the time or were older stories that had never been printed before.