is there are way to use a webbrowser control with a genuine IE7 or IE8 render engine?
Yes, but it requires that you downgrade the version of Internet Explorer that is installed on the computer to version 7 or 8, which doesn't make for a friendly installation experience.
The issue is that the WebBrowser control always uses the version of IE that is installed on the computer because it simply delegates rendering to the native library shdocvw.dll, the same one that is used by IE itself. In your case, that appears to be IE 9. However, by default, it also runs in IE 7 compatibility mode. You can change this by editing the registry, but you cannot change the version of the rendering engine.
And unfortunately, this means you're out of luck, because running multiple versions of IE on a single computer is not and has never been a supported configuration. It can be accomplished for testing purposes, but it requires additional software and the versions don't play nicely together. Certainly not nicely enough for one to support the standalone IE browser while the other drives the .NET WebBrowser control.
Fixing the code to work properly with IE 9 is the best option. IE 9 represents Microsoft's slow progression towards a standards-compliant browser, and although it still has some quirks, it is worth supporting. I know you said that the website code is maintained by "someone else", but I recommend filing a support request with them—their code is buggy and needs to be fixed. If you (or they) need help with this, they can ask some of our code ninjas web standards experts here on Stack Overflow.
Alternatively, you could explore replacing the WebBrowser control with an alternative control. There are several good ones for the .NET Framework, wrapping the rendering engines used by other popular browsers. For example:
- WebKit .NET is a wrapper for the WebKit engine, used by Google Chrome and Apple Safari.
- GeckoFX is a wrapper for the Gecko rendering engine, used by Mozilla Firefox.
- MozNet is an alternative wrapper for Gecko.
Unfortunately, if the code you're dealing with is so badly written that IE 9's feeble attempt at standards-compliance brings it to its knees, it's unlikely that switching to the rendering engine for another even more standards-compliant browser will bring much success.