4-5 just import it into 5.

For 6-5 you have to open up the file in note pad. look at the top:
it should say: requires maya "6.0";
or something else like that. the one with // in front of it you dont have to worry about. change the 6.0 to 5.0 so it would be:

requires maya "5.0";

You might lose some data. hardly anything noticable.


have fun!