the trouble with baigent and leigh is that they're not terribly well respected as historians with, by most standards, a tendency to make huge assumptions and leaps in logic, plus a regrettably tabloid approach to history, you know, "THE BOOK THEY DON'T WANT YOU TO READ!!!!" sort of thing.
my own opinion on the dead sea scrolls is that the qumran sect were, well, sectarians, basically jewish but ascetic (which is a bit problematic in judaism) with about the same relationship to mainstream judaism as, say, charismatic pentecostalists do to the archbishop of canterbury - disreputable but not quite heretics. the group that eventually became the early church may or may not have been the qumranis (or the essenes) and may or may not have been mates of theirs. at any rate they would undoubtedly have known of each other even if not in contact or on friendly terms.
the thing that interests me a bit more is the accusation that the dead sea scrolls have been "suppressed" because they contradicted the new testament or bits of the old testament. now NT suppression is not my problem, but OT is, so i once asked a dead sea scrolls scientist if it were possible that textual variations could be explained by their being private scrolls (you're not allowd to emend public ones) and he said yes, that it was perfectly possible. also, incorrectly written scrolls shouldn't really be used, they should be buried, i believe. which i think these were.
just my two penn'orth.
b'shalom
bananabrain