I may even stop over at the religion department at McMaster and see if anyone is doing research in this area. I will get back to you with my results.
Cool. But you are right (I searched around the net now a bit): Christians probably did tamper with Josephus` works. Only, I am not sure about how much they tampered with it. I seriously doubt that they just inserted everything in that short passage about Jesus. No, I think Josephus DID mention Jesus, but that he mentioned him in less favorable terms. You know, my main argument (or thought, or whatever) against your claim that this whole passage is fabricated and inserted later, is that: If there was something in this "conspiracy theory", that christians in the 4th century had fabricated this passage in Josephus to support their belief in the Jesus-legend, then these christians would have had to have a reason for doing so. Either that they themselves were in doubt about whether or not Jesus actually existed, or that others were saying that he never did, neither of which is very likely. Like you yourself said, this "cover-up", if it indeed did happen, would have had to have happened at a time when christianity had allready come to power. And if they had allready come to power, then why would there be a need to insert this passage into Josephus in the first place? Also, if they did tamper with Josephus texts, then why didn`t they do a more thorough job than they did? Why didn`t they write several pages about him? Or a whole book, and present it as Josephus "contemporary testimony of Jesus"? They could have easily have gotten away with it (back then).
I think the truth on this is somewhere inbetween, because you are right (I`ve searched around the net a bit): Christians probably did tamper with Josephus works: But they probably just changed what Josephus had written about Jesus a bit, they didn`t just shove Jesus into a text in which he wasn`t mentioned in the first place. The most probable scenario is that Josephus mentioned Jesus in less favorable terms, and that the christians later changed this:
http://ccat.sas.upenn.edu/humm/Topics/JewishJesus/josephus.html