The following was posted to start this thread in the ArsTechnica forums:
It took some work, but I was able to get a working (if a bit buggy) version of IE6 running on OS X via WINE. I used the installer script from IEs4Linux. After resolving its dependencies, it ran through the IE6 install just fine, then hung during the IE5.5 install, at which point I killed it.
If I remember correctly, the version of WINE I am running was obtained here (but don't quote me on that, I installed it a while ago). I installed cabextract using DarwinPorts (because the version available through Fink was apparently too old).
Should be fairly straightforward, thanks to the IEs4Linux installer script. Enjoy!
Further into the thread, there's a post by bupkis with a more detailed version of the instructions, which will probably prove helpful if you're going to try this.
[robg adds: I haven't tried this one, and with Parallels Desktop running IE6 (and IE7 betas) very nicely, I probably won't use this hint. The advantage of this solution, however, is that you won't need either Parallels or Windows to run IE6, thereby saving quite a bit of money.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=2006060201470077