How to add objects to FS2002 & 2004??

Ok this might be a general question but iv searched everywhere and cant find it. I want to add objects to an already exsisting default scenery in fs2002 and 2004 like hangers , passenger walkways, Vehlicels ect. How would i do this? i can do it with fs2000 but theres something different with the current flight sims??? i dunnno...can someone give me a list programs that actually work? especially for FS9. thanks