Well, finally beat this scenario (Regent, Erik Bloodaxe) with a VP victory. You were right, KingArthur, sacking and taking LOADS of captives were the way to go. I actually had a constant stream of booty going to the capital throughout the game--those Raiders are perfect for carrying it away at high speeds over roads.
Wound up taking out Northumbria and Mercia first, then East Anglia (although they escaped with a settler and put a city in inaccessible area--well, inaccessible unless you wanted to go through several civs to get them). Strathclyde was attacked and largely beaten by the Scots, who I helped and almost killed them off--they also escaped with a settler but never founded a city. Bluntnose Vikings then declared war on me for no reason, I smacked them down, and then declared war on the Welsh. Took several of their cities, raided Wessex and one of the Irish groups, and then on to victory.
Some basic points: I have to say, this is a great scenario--and very tough to beat if you're trying for a conquest or even domination. Wessex was for some reason really powerful, they keep building S#@loads of horses and just wasn't worth the effort attacking. And they expand better than the other civs as well (which is historically good). The French Vikings, as well as the Irish ones, seem like their next easiest; the two northward ones seem toughest to win with in this scenario. I think they might require lots of raiding at first.
And you CAN kill kings with raiders, you just need a lot of them. One way is to wait for the AI to start walking its kings around your territory--for some reason I had the Picts, Strathclyde, and Scots kings walking around as easy pickings. Another thing I found--the AI doesn't know your nationality if you have a raider army--or in my case, LOTS of raider armies. This was a really fun part of the scenario.
That being said, the AI--unlike in some other mods--WILL attack your armies, even if they're relatively strong (but never if they're near-perfect health).
Great job!