it only creates that user / pass combo if you go into the creation script and tell it to create that. The horde, imp, and kronolith mailing lists and archives can give you a lot of insight into some of the issues you might encounter.
just check the create sql script that you ran, and near the top, check to see the user/pass it created to access the db's.
Also, you may need to add a user to the horde user database. It's been awhile since I played with it, so my mem is a lil fuzzy...