Cross-browser compatibility is one of the most flaming issues in web development (for everyone from professionals to bloggers tweaking themes).
Internet Explorer is often (but honestly not always) main source of issues. If properly updated Windows tries to install latest stable version of it. That can actually make harder to look into issues that only show on earlier versions.
Internet Explorer Collection is bundle that installs multiply IE versions at the same time.
What it does
Internet Explorer Collection is more of installation package than actual software. It comes as single setup executable that installs multiply Internet Explorer versions from 1 to 8 (you can select which exactly you need) as long as they are compatible with Windows version you are using.
- run different versions at the same time;
- installs separately, doesn’t affect native IE;
- comes with developer toolbar;
- actively updated with latest version compatible with everything up to Windows 7.
Probably easiest way to have several IE versions installed for testing purposes and also stays away from system files.