It does mean if he were on Earth now. Flemming totally misuses that verse in his movie. He leads the viewer to believe that this was a verse written by Paul. In fact, Paul did not write the book of Hebrews. Then he takes the verse out of context to lead the viewer to an incorrect conlcusion. Great intellectual honesty from Brian Flemming!

Additionally, Jesus was of the tribe of Juda.  Priests were required to be of the tribe of Levi.

The God's Word version, a thought-for-thought translation, renders Hebrews 7:3 as follows:

No one knows anything about Melchizedek's father, mother, or ancestors. No one knows when he was born or when he died. Like the Son of God, Melchizedek continues to be a priest forever. (emphasis mine)

This, at least, is how the first century Jewish mind would understand the use of "without father, without mother, without geneology" in Hebrews 7:3.  Why? Because of the rabinncal argument from silence.

In rabbinical logic and reasoning, statements could be made which were "arguments from silence." If the Bible didn't specifically say something about a person, place, or incident, various conclusions could be drawn for the sake of the claim or discussion being presented. The author of Hebrews (probably Paul) was obviously familiar with the law, the Temple service, and forms of rabbinical discourse. He uses the rabbinical method of argument from silence in verse 3.

... Thus, Melchizedek could be said to be "without father,without mother, and without genealogy" because the Scriptures didn't identify his lineage. While this argument might seem unconvincing to the modern mind, it would have been understandable and reasonable to a first century Jew.(source)

This same argument applies to Melchizedek being without beginning or without end, and continuing in the office of priest. 

Well then, you should tell those pastors that they are wrong. Hebrews was not written by Paul. You can research it for yourself online. I've even heard Richard Carrier say that Paul did not write Hebrews. 

I disagree Cory T. Hebrews 2:3-4 makes the claim that the author recieved the Christian message from others. In Galatians, Paul claims to have recieved a vision from the resurrected Jesus.

Furthermore, the style of Koine Greek is much different in Hebrews then the authentic letters of Paul such as Galatians or Romans.  

Also, for Christians it's cannon either way, so it doesn't matter who wrote it. Unless you support the historical perspective to a point that will necessarily vacate the Bible of any presence of the transcendental.

I'm a Christian pastor. I think that Luke may well have written Hebrews. Although it is pressing the matter too far to say that we know for certain that Paul did not write it, it is not credible to suggest that every Christian pastor is committed to Pauline authorship of Hebrews.

Also, I've got my Greek New Testament open to Hebrews 8:4. This is a second-class conditional sentence out of standard Greek grammar. Such sentences express a contrary-to-face protasis (if-clause), followed by what would be the case if the hypothetical condition were met in the apodosis (then-clause).

The rhetorical importance of the sentence is simply this: The author is asserting Jesus as the great High Priest of all time, and yet Jesus of Nazareth was not any sort of a priest at all (for the genealogical reasons indicated above). That's a serious objection to the line of argumentation in Hebrews, depending as it does so heavily upon the idea of the priesthood of Jesus Christ, and the author is going out of his way here to address it.

So, ironically, at that time opponents of Christianity, rather than denying the historicity of Jesus, were using the facts and details of the historicity of Jesus of Nazareth as key elements of their arguments against the idea that Jesus was God incarnate bringing salvation to mankind. It is quite difficult to imagine the need for this sentence apart from the idea that both the author and his anticipated opponents had heard and had received as fact the idea that Jesus of Nazareth lived, was not a priest of any sort, and was the central figure of the Christian faith as advanced by this book.