In Vault objects have a property called path. I like to use the property in a rule when determin which category the part is.
If path contains "LIBRARY" category_name = "Library parts"
If path contains "DESIGN" category_name = "Design parts"
If path contains "Content Center Files" category_name = "CC parts"
In this way a user only has to place the part at teh right location on disk. During initial check in it will get the correct category automaticly.