Anthrax, weaponized in the manner of the sample sent to Majority Leader Daschle, is an almost perfect weapon of mass destruction. A suitcase full of it could kill three million people -- 10-100X more than one of the "suitcase nukes" we are all supposed to be worried about. Unlike a nuclear weapon, which gives off tell-tale radiation, there is absolutely no way to detect an anthrax stash remotely. Unlike a nuclear weapon, anthrax has an essentially infinite shelf-life. Unlike a nuclear weapon, anthrax can be handled safely without elaborate safety precautions; it only needs to be kept in a sealed container until use. And, like a suitcase nuke, anthrax can be delivered to its target on foot or by automobile -- no ICBMs required.
For all the above reasons, it was not very smart to pull our weapons inspectors out of Iraq three years ago. It looks like the genie is out of the bottle. Forget about arms control. No treaty, no inspectors, no verification is going to do anything about this threat. Game over. We are f***ed.
But I don't think this analysis is right. If this is what he's trying, it's intolerable to us, and we will destroy his regime. Yes, he may distribute some anthrax, and the results may be terrible, but they will be temporary, and he will lose; after his loss, he will be reviled throughout history in the Muslim world for the destruction he brought down on them. We need to make absolutely clear to him that this is what will happen, and possibly he'll be deterred.
In another sense, though, the problem is deeper than you're suggesting. Technology is changing the balance of power in the world; small groups of people and relatively weak countries can now command huge amounts of energy, increasingly huge as technology advances. There is no actual defense against these kinds of attacks; the only defense is offense. I'm afraid this will require a continuous staying action, and I don't know if it will ultimately be successful, over, say, the next century.
This is what happened when the Roman Empire fell and Europe entered the Middle Ages. Power couldn't be effectively projected over large areas any more, because of technological changes, and Europe split into many small fiefdoms. This slowed progress dramatically (more borders limit trade, they limit communication, they reduce the spread of new ideas, etc.). (I believe similar changes happened in China at about the same time, lending credence to the idea that this was driven by technological changes. It's been a long time since I've read Chinese history though, and I'd have to look it up again.)
Needless to say, I hope this analogy is wrong. Maybe we can learn from history so it comes out differently this time around.