you need to go into some of the finer details of a story etc.

after that i suggest you read some articles onwhat it takes to make a mod

setting up a FTP, irc channel , and site etc. , you might also want to consider it takes a long long long time to complete a mod, then when that is done, you need to find a team, who is dedicated , and is willing to spend years crammed into their litle pc rooms working on the mod, without getting anything out of it except some experience that could be gainded making just normal sp maps

but if you realy want to do this, i wish you the best of luck, go do it , and do it good

http://www.nma-fallout.com/article.php?id=9008

i suggest you read that if this is your first mod, witch it probarbly will be