[ejones]

That exists, it's called 'Compatibility Mode'. And by default (at least in IE8, at my current client's deployment) it uses it for all Intranet Sites. You can also use meta-tag 'X-UA-Compatible' to force a certain compatibility (http://msdn.microsoft.com/en-us/library/cc288325(v=vs.85).as...)

EDIT: Apparently the best you can do for IE6 is to 'emulate IE5,' which actually means 'emulate IE7 quirks mode'. Oh well...

[JonoW]

Compatability mode doesn't support ie6, and I believe its only for the renderer, not the JavaScript engine.

[yuhong]

It is for the JavaScript engine too: http://msdn.microsoft.com/en-us/library/s4esdbwz(v=VS.85).as...

[ejones]

Yeah, it doesn't seem to be a complete solution. My client actually ended up deploying a virtualized IE8 to sit alongside IE6 on all workstations.