Google Chrome Frame is a neat idea.
For an answer to your first question, you can absolutely prevent IT from installing plugins. Here is the GPO area:
- Allow third-party browser extensions: Windows Components\Internet Explorer\Internet Control Panel\Advanced Page
- Add-on List: Windows Components\Internet Explorer\Security Features\Add-on Management
- Deny all add-ons unless specifically allowed in the Add-on List: Windows Components\Internet Explorer\Security Features\Add-on Management
I don't think Google can get around this, at least in the plugin arena. However, I thought I read somewhere that Chrome's installation program is pretty novel, in that it installs itself in a user's own area and not the system, meaning it installs (on XP) in c:\documents and settings\username... rather than c:\program file.... You might find that you are able to install the normal installer, depending on your GPO settings.