http://www.microsoft.com/downloads/details.aspx?FamilyID=e41d8800-d134-4356-a2e7-c01bee790908&DisplayLang=en

This guide helps you to plan and carry out a deployment of Microsoft Internet Explorer 7 on Windows XP and Windows Server 2003. The guide describes the system requirements and deployment methods, as well as the techniques to maintain and support Internet Explorer 7 after deployment.

Wow. That was frighteningly simple. The client's think they are getting a security update just like they normally get, and BOOM! IE7 is installed.

Of course, I did everything with local administrative privs. Tomorrow, I try all of this again with user privs. This has been a stumbling point with IE previously, since you had to have administrative credentials to log in the first time after reboot for everything to go well.