Running as Limited User – the Easy Way
Mark Russinovich created a utility called PsExec that allows you to run programs as a limited user. A little work and you'll be running both Internet Explorer and Outlook in a mode that would severely limit the vulnerabilities in each of these applications. Unfortunately, it requires a little bit of technical knowledge to setup. I'm hoping Mark will allow me (I sent him an email) to create an installer that'll make the setup a little easier.
http://www.sysinternals.com/blog/2006/03/running-as-limited-user-easy-way.html
As far as I know, this same function has been available in Hitman Pro (www.hitmanpro.nl) antispyware engine for some time now (called SurfRight) and requires no work on the user’s part (available as an option when installing spyware protection via Hitman Pro).