With my 8830, I go to my phone book and find the contact I want to set a ringer for.
When the contact is highlighted, I hit the menu key and scroll down to "Add Custom Phone Tune" -- this will set a specific ring for a specific contact.
Good to know. I have not really used special ringers other than changing the default one. Nice to know I can set up special one's so I know which call to get and which to ignore.
Some of the "non standard" or mp3's are really quiet unless you or someone has altered them to play louder. Just because it plays loud in the media player doesn't mean it will be a loud enough ringer for you. I missed a couple of calls because of this.