The main reason that people use Internet Explorer in Crossover is to access "IE-only" secure websites/webapps. These websites can be configured to call on a wide variety of windows components (particularly if they use ActiveX controls), and in some cases the components needed by a given function or tool on a website may not be implemented in Crossover. Because of this, there are some secure "IE-only" websites that don't work properly, or at all, in IE-via-Crossover.
To see if your website will work in Crossover, you'll want to try both IE7 *and* IE6. We've encountered a number of websites that function better in IE6 than IE7, and just as many that function better in IE7 than IE6.
You can install both IE6 and IE7 from Crossover's Install Software menu. Simply select "Internet Explorer 6.0" (or 7.0) from the list of supported software, and then click "Install" to proceed with the installation. Both installations will require that you approve the installation of a number of different windows packages - all of these are necessary, so you'll want to approve any prompt that pops up, and choose the default options given to you (i.e. "typical install" instead of "custom install").
By default IE6 and IE7 install into different bottles, so you can have both versions installed on your computer without one interfering with the other. When IE has been installed, the Internet Explorer launchers will be inside "Programs>Accessories" (on Mac) or "Windows Applications>Accessories" (on Linux). The IE7 icon also looks a bit different in that the circle around the "e" is yellow, whereas the IE6 icon is entirely blue.
An additional package that many users find necessary to use with IE6 is the "Flash 9 ActiveX Control" package. To install this into IE6, go to Crossover's Install Software menu, expand the "Runtime Support Components" section, and select "Flash 9 ActiveX Control". Next, click on "Select a bottle", and select your pre-existing "Internet Explorer 6.0" bottle. Click on "install" to proceed.
You can also download Crossover Office 8.0.3 and run IE6 in it as a last resort. Crossover's IE6 support was optimized for this version, and thus IE6 in CX 8.0.3 works better for some users (IE7 will not be any better in Crossover 8.0.3). You can get Crossover Office 8.0.3 by logging into your account, go to My Downloads, and the Archived Downloads tab.