Another n00bie question

I see that theres more then 1 db, i have a few questions about them.

1.) What are the diffrenices between them all, is there custom items and mobs or are some more compleate than others, ect...

2.) Can you have more then 1 db running on the server at a time, or is it one at a time.

3.) This is like a follow up to question 2, If you can use more then 1 db, can you get only parts of the of the db running, or do i have to use the full db even though it has broken zones (i.e. cant log into gfay). If you can use just some of the zone that are in the db I would like to know how I can trunicate to the zones/items/quests that i would like.

4.) Are there any easy tutorals on worldbuliding, I know VB, C#, and I know my way around some asm calls. If these have any impact on worldbuliding I would also like to know about haveing some programs that are opensoruce that I can look at to get a feel for whats happening around the emu at world compile and loading at the db(I sleaped through the chapter about databaseing/info calls to exteral programs in secuered connections and we dont use anything like that at where I work[Adobe].

Any help and/or info would be appreaciated, Thank you