I can save POIs to my Garmin c550. They show up under my "Extras" button. No problem. The issue I have is that I would like to group them into different catagories --"Malls" "Restaurants" "Attractions" and etc., similar to the way the preloaded POIs are presented. Can this be done?

You can have them show up in
You can have them show up in different POI databases (malls, etc) thusly:
Keep them in seperate files:
restaurants.gpx
malls.csv
Before invoking the poi loader. The GPS will, based on my tested and reading, will keep them in seperated DBs although under the hood in \garmin\poi they are really one file.
You can keep multiple poi files in that dir if you really want to.
US-only CoPilot + android Optimus T = cheap, effective nav http://www.mousetrap.net/mouse/gps/