I just bought the HTC Droid Eris and i updated my software to the 2.1 firmware and i was wondering how do i add ringtones and can the mp3 songs i upload to my phone be used as ringtones.
Yes mp3s can be used as ringtones. You can put ringtones on the phone by transferring them to your phone when its connected to your computer, or by downloading them with an app like Mabilo
you can add 30 second clips of songs to your phone's memory card and use them as ringtones, or even better, a feature of 2.1 allows you to play a song, and if you hold down the menu key I believe it let's you create a ringtone from the file on your device.