That's what I was thinking. But I don't want to buy something without asking someone that knows.
I have seen 1.5m 800 to 400 cables on Ebay.
I will probably order one of them.
I don't mind if the 800 port runs at 400. The 800 port is on my external drive and the 400 is on my PC.
If it works I,m happy.
It will be cheper than having to buy a FW800 PCI card.