Yes, I know the headline sounds like the fodder for a joke: "Run IE on Linux? Why would you want to?" But there are circumstances where it's unavoidable -- compatibility testing, or accessing IE-only sites without dual-booting -- and in the last few weeks I've come across a couple of interesting approaches to this issue.
The first approach is a script called IEs4Linux by Brazilian programmer Sérgio Luís Lopes Júnior, which is essentially a way to install IE from its original cabinet files and run it under Wine. Specific instructions are included for all the major distributions -- Ubuntu, Fedora, Debian, SUSE, PCLinuxOS, and others -- and each step of the instructions are spelled out in clear detail. IE7 isn't fully supported, but a beta version of the script accomplishes a nifty trick -- it places the IE7 rendering engine inside the IE6 user interface. Keep in mind that in the disclaimer for the project notes, it's mentioned that you need to have at least one valid Windows license to install IE to be in full compliance with the EULA. (I also imagine it's now that much easier to pull all this off since IE7 no longer requires WGA to work.)
Another way to run IE on Linux comes courtesy of Microsoft itself, sort of. If you're running Microsoft Virtual PC or using VMWare (which can convert Microsoft's .VHD format) you can download a virtual machine image from Microsoft that contains a preactivated installation of Windows XP with Service Pack 2, preloaded with your choice of Internet Explorer 6 or Internet Explorer 7, and use it in the VMWare Player. The image in question is timed to expire on Dec. 7, 2007, but I've seen previous editions of this VHD offered before, and each time it's about to expire Microsoft has offered a refreshed version which times out in about 4-6 months.
If you've got other approaches to this particular problem (sorry, "just use Firefox" doesn't count here), feel free to share them.