Internet Explorer 7.0 Beta 2 is out, and I'm not going to install it - I just paved my machine, and I don't want to throw it to the beta-wolves.
Fortunately this version supports the same hack as the previous. Download the Beta EXE here and unzip it. It's an EXE, but it's a ZIP, so create a folder and unzip the contents into the folder. There will be an UPDATE folder that you don't need that can be deleted.
Create a file called iexplore.exe.local and put it in the same folder. It doesn't have to have anything it in. You can do this from the command line like this:
copy con iexplore.exe.local
...then press Ctrl-Z. Now you can run IE 7 Beta 2 without having installed it (see image above).
OK, REALLY, FINAL UPDATE: This messed up my system as well such that clicking links in IE would open them in FireFox. While a neat trick, suboptimal at best. Thanks to Jon Galloway, I fixed it with this .reg file that deletes some tumor in the Registry:
Windows Registry Editor Version 5.00
UPDATE: From the IEBlog "As Chris Wilson pointed out, "'IE' is actually a collection of system components - networking, browser hosting, core HTML rendering, printing, etc. When we install a new version of IE, we're installing it for all applications that use these system components - including the tiny iexplore.exe itself." Because of this, we do not support the various hacks that allow side by side running of IE6 and the IE7 Beta 2 Preview. Running with these could cause issues with the stability of a system.
So, seriously, now I'm sorry I even mentioned it. ;) Your Mileage May Vary. I recommend hanging back while we learn why this is all so hard.