hOW to costomize ring tones for different contacts.

Offcial Managing Ringtones Info

You can use  Ringdroid to cut a section of an MP3 for a ringtone or notification tone right on your phone.

If you create the following directory structure on your phone you can put tones longer than the supposed at&t limit in them and the phone will recognize them:

sdcard
  \media
     \alarms
      \notifications
       \ringtones

Where ringtones and notifications are sub-foders of media in the sd card root.

Rings Extended may be useful if you don;t want to move your mp3s.

You may want to look at RingoLite.