As Mike said, you can batch update threads in the Applications tab of the Admin CP and choose to batch update threads created by a specific user.
For managing it in the future, aside from enabling flood control (which should always, always be turned on - the completely minor inconvenience that a user will have by waiting 10 seconds to make a post is invisible compared with the major problem that a spammer with no flood control can cause), I've installed FoolBotHoneyPot, StopHumanSpam, and pay $5/month for an Akismet subscription. This has basically eliminated all spam in our forum.
We're blocking 80-150 bots per day from registering, the couple that get through and try to make posts have their posts placed in a Moderated queue, and the StopHumanSpam plugin prevents bots that register from quietly adding links to their profiles or signatures.
It's pretty outstanding. I went from managing 20-30 user-visible spam posts per day, another 10-50 spam user profile posts per day, and an unknown quantity of bots with spam signatures (which I was manually purging at monthly intervals), to 2-3 spam posts per day that are all caught and put into the moderated queue.