I've finally gotten the hang of the Microsoft Script Debugger. I can now debug Ajax code in IE with relative ease. Before this, the error line number IE gives is always wrong, so there's no good way to know what is wrong with your code. I tried firebug lite, which provides the console, and is handy, but it has no debugging capability. The Script Debugger is very different from firebug, so you have to get use to it, and even maybe read the help pages. But once you figure out, it's very helpful, well because you are comparing it to having not debugger or a use full stacktrace message at all. It does have a command window, which is kinda different from firebug also, but once again, you can get used to it. And the call stack window is very useful for spotting where an error has occured.
Negatives: it does crash a lot, as with everything Microsoft. And once it had a bug where the included javascript files in the page would not show up at all. It was eventually fixed I think after a reboot. Still, better than nothing.