<p>In Google Chrome, I can provide the command-line argument --user-data-dir="..." to have Chrome use a different directory for state like cookies, cache, and so forth.  This makes it possible to trivially load web pages from a "fresh" browser and simulate multiple independent users.</p>

<p>How can I do the same thing with Internet Explorer (either 6, 7, or 8)?</p>

<p><strong>Edit</strong>:  It's looking like IE always uses the current user's profile, so you have to set up multiple users on the system and switch between them.  What a pain.</p>

Heh.
With Chrome, FF, etc. I can actually have multiple
versions
on a single machine and test them without interference. IE requires me to set up VMs. Hence, the bulk of the code i churn out only gets tested rigorously on IE6 (since that's the install on the host OS). IE, if you'll pardon my slang, is a bitch - i've no idea how they manage to test it effectively within MS.
That said... You can
sort of
get what you want. If you're running XP and
aren't
on a domain, or are running Vista, you can configure "
Fast User Switching
". Then, configure multiple user accounts. Finally, log into each one, launch IE in each one, and rest assured they're using different profiles / data directories. Alternately, if you're running one of the Server versions of Windows (i'm partial to 2k3 r2), you can set up Terminal Services and simply use
RDC
to create multiple concurrent logins.