Thanks again for the all advice everyone. Some really great information in this thread.
I'd always had the impression that building permits where really expensive and that building inspectors were 'the devil'. But as it turns out, they seem pretty friendly, knowledgeable and reasonable.
After talking again with the building folks, the impression I'm left with is that adding risers wouldn't require a building permit and I wouldn't need to bring the entire deck up to code. Just the risers.
The permits are also a lot cheaper than I'd expected. $25 dollars for a project valued at $500 or less (it scales up beyond that). And, even if you don't need a permit, for $25 dollars you can go through the process and you get an inspector to make sure that what you are doing (and the things around it) are safe and done correctly. It actually seems like pretty good deal.
My plan now is to add the risers (since I've already bought and hauled the lumber). But my deck is tiny (5x5 maybe - and stairs). So, what I really want to do is rip it down and build a new, bigger, nicer, up-to-code deck.
Cost is an issue - so it'll probably happen next spring; but I think it'd be a lot of fun.
EDIT: Not a very good picture - but I've added the risers. Ignore the mess, there is a lot of cleanup to be done