You can create custom forms for adding and editing items in a collection via the following lines in the CollectionDefinitionFiles:

add = form:news/add
edit = form:news/edit

Each points to either a form or a box (the "form:" text followed by the form or box name) that you would write. Usually I simply copy one of the existing forms and base new ones on that. I usually like the sitellite_news collection's add/edit forms for this since they're cleaner than some of the others.

Note: Make sure to copy the edit-top.spt file from inc/app/news/html into your own app's html folder and adjust the height value in the file (in 5 or 6 places -- this should be made a parameter...) if you want the edit/properties/state tabs.