What do you mean with 'arduino 1.0' ? I hope not the IDE, since that doesnt have to do anything with the opening of multiple files.
It depends on the lib, but i haven't seen any lib that can open multiple files at once, i suppose you'll have to do it the 'hard' way and open them one after each other.
opening files has a need to keep pointers to the file object, and i think that if you use multiple pointers it will get mixed up