Contact the high school and ask to talk to the music teacher or director. Either one may be able to check the records and find out what music was played at that time, including a copy of the graduation program.
Ask a school administrator or teacher if there is a recorded copy of the graduation that you could watch to in order to get more of the lyrics when the song is played, or if she knows if the same songs are played at every graduation.
Ask people who had attended that graduation including friends and family, if they know the song. Check with your contacts on Twitter, Facebook, MySpace or other online social network to see if they know of or have heard the song.
Use a lyrics search website by entering the words you remember in the website search box. Click search and read the lyrics of the songs suggested.
Plug the words of the title, if they may be what you remember, into the search of a music download service such as iTunes or Napster. Play samples to see if the music matches what you remember.