If you first deployed IE8 via a gpo do this:
1) Start the Active Directory Users and Computers snap-in. To do this, click Start, point to Administrative Tools, and then click Active Directory Users and Computers.
2) In the console tree, right-click your domain, and then click Properties.
3) Click the Group Policy tab, click the Group Policy object that you used to deploy the package, and then click Edit.
4) Expand the Software Settings container that contains the software installation item that you used to deploy the package.
5) Click the software installation container that contains the package.
6) In the right pane of the Group Policy window, right-click the program, point to All Tasks, and then click Remove.
Do the following:
7) Click Immediately uninstall the software from users and computers, and then click OK.
8) Quit the Group Policy snap-in, click OK, and then quit the Active Directory Users and Computers snap-in.
If you did not publish IE8 via gpo try to execute %windir%\ie8\spuninst\spuninst.exe with /s (for silent)
via a gpo that would execute a script at logon.
