An alternative to virtualization (which is already covered in other answer) would be to use a Windows runtime environment emulation such as Wine (free & open-source).
PlayOnMac, the Mac version of PlayOnLinux, is a free graphical frontend for Wine and provides configuration templates to run the windows version of Internet Explorer.
Alternatively, you can also install and setup Wine manually. It's mostly dedicated for advanced system administrator but there is a packaged commercial version called CrossOver with customer support if you have some money to spend.
Although those solutions have a lot of benefits (no virtual machine, no Windows license needed, no cost), they may be really tricky to set up if it doesn't work out-of-the-box. In which case a windows virtual machine may be the easier way to go.