C# – ActiveX running Issue on Vista

I wouldn't do it. Use virtual PCs instead. It might take a little setup, but you'll thank yourself in the long run. In my experience, you can't really get them cleanly installed side by side and unless they are standalone installs you can't really verify that it is 100% true-to-browser rendering.

Update: Looks like one of the better ways to accomplish this (if running Windows 7) is using Windows XP mode to set up multiple virtual machines: Testing Multiple Versions of IE on one PC at the IEBlog.

Update 2: (11/2014) There are new solutions since this was last updated. Microsoft now provides VMs for any environment to test multiple versions of IE: Modern.IE

In order to run in IE, you also need to implement IObjectSafety so that IE knows that it is safe to be called by an untrusted caller and/or with untrusted data. (If it is actually safe, that is)

Personally, I have only done this in C++ & ATL, not C#, but here is a blog post that looks like it should help you achieve this in C#.

http://blog.devstone.com/aaron/2007/06/12/ImplementingIObjectSafetyInNETMarkingClassesSafeForScripting.aspx

The reason for this is that scripts by nefarious individuals may use your object to bypass the normal security offered by IE, so your ActiveX Object must defend against untrusted pages itself.

When you sign a cab, you are telling the user that the cab they are downloading is the one they think they are downloading - i.e. that some malicious individual hasn't replaced your cab with a dangerous one. If they trust you as a publisher, then they can trust that the ActiveXObject will not do anything evil on its own, or in combination with other code that they trust.

When you implement IObjectSafety, to return INTERFACESAFE_FOR_UNTRUSTED_CALLER | INTERFACESAFE_FOR_UNTRUSTED_DATA, you are telling IE that the object cannot be used maliciously by anyone else, and is therefore safe to run in conjunction with code that the user doesn't explicitly trust.