Are my principals actions legal?

I am a senior at a private Lutheran high school, which is very very small. Recently, a student came to our principal complaining about a conflict that was happening on myspace and some other online forums. He gave your principal the pword to his profiles. My principal logged on and viewed everybody's profile from my school. I was forced to delete my myspace profile, even though it is set to private. The reason was that it had 3 swear words on it. He said it makes our school look bad, even though I don't even say where I go to school on my profile. Because of this, I had to delete my profile, as well as an account on another website called opendiary.com ...I was told that if I am caught having an account on either website again I will be expelled. I also found out that he had been reading my online diary for at least a few weeks before I deleted it, which in itself creeps me out. But anyway, are his actions legal? If not, where can I get more information? What can be done about it?