One of my (and my Evil Twin Katherine's) pet peeves.
Xena and me are going to Athens. --> INCORRECT
This horse belongs to Xena and I. --> INCORRECT
"I" is a pronoun that must be the subject, never the object, of a verb. "Me" is a pronoun that must be the object, never the subject. (The same is true for he/him, she/her, we/us, etc.)
As a simple test, try removing Xena from the sentence. You wouldn't say "Me is going to Athens." You'd say "I am going," so say "Xena and I are going." You wouldn't say "This horse belongs to I," you'd say "This horse belongs to me," so say "This horse belongs to Xena and me."
Contrary to the belief of Katherine's friend John, "Xena and I" is not always correct.
Source : http://www.englishchick.com/