You can refresh your search cache (I advise doing this in a fresh Single Player game) so that you can just search the model name instead of going through the Browse tab every time you're looking. If you don't know of the button, it's the green recycle symbol on the main tab (the one with the spawn list and props) next to the search bar. As Nesstea/Ves said, you can use the browse menu, but if you refresh your search cache, then you can just search 'group01' and you'll get all the files in the 'group01' directory. If I remember correctly, group01 and group02 are used for the citizen models, group03/03m for the rebel/medic vest models, and group04 is for some of the special models (Lambda models, for example). I dunno how things have changed since I left.