Okay, but I still see two problems:
1) If the thief died under the "old" covenant, wouldn't he need to offer an animal sacrifice to be cleansed of his sins? Or, if faith without baptism made one righteous before God as it did in the case of Abraham (Gen. 15, Rom. 4), why would it become an added condition under the new?
2) Baptism for repentence was instituted by John the Baptist, not Jesus:
And he said to them, "Then to what were you baptized?" And they said, "To John's baptism." And Paul said, "John truly baptized with the baptism of repentance, saying to the people that they should believe into Him coming after him, that is, into Jesus Christ." --Acts 19:3-4Therefore, if baptism is required for repentence rather than being a sign of it (which is the predominant Christian view), the thief was still hosed by not receiving it, since it had been instituted by God through John over three years before.
1) As I stated, Christ could forgive anyone he chose to forgive. I can not for sure tell you why baptism is required in the New Testament, I just know that the Bible so teaches. In baptism, we are buried and raised to a new life, which parallels what Christ has done for us. It is not the water that does anything, it is our submission to the will of Christ.
2) There is no proof that the thief on the cross had not been baptized by John the Baptist. The Bible clearly states that many in the area were baptized, so he very easily could have been one those who had been baptized. Either way, the fact is Christ had the power to forgive sins while He was here.