Dunno if it was ever a TV series, but they borrow pretty heavily from a book called The Holy Blood And The Holy Grail:
Amazonian Clicky
For what it's worth, I thoroughly enjoyed it. There are some parts of the plot that are holier than a Swiss Cheese - I won't go into them in case I spoil anything - but still an enjoyable yarn, and really helps you picture certain scenes that were hard to imagine in the book.
I'd give it an 7, but I got a BJ after it, so we'll call it a 8