It should be in the add/remove list. Well, my neocodex files are at least.
If not, try running the uninstaller in your neocodex folder. I never use the uninstallers in my add/remove list unless I can't find the actual uninstallers.
Oh, I did find Abrosia in my add/remove list at last. But it was named after "UninstAbrosia" or something, that's why I overlooked it at first sight.
EDIT: I'm having the same problem as moosejuice, but I guess it's something related to Vista, because I tried running Abrosia on a XP and it worked just fine.