You’ll need to download the Windows Phone 7 simulator from this Download Link. This only works for Windows Vista and Windows 7.
The downloaded package comes as an .exe file and just run it to install. Once done, click on the “Internet Explorer” link.
Note: the simulator does seem to require a fairly decent PC (or laptop) to run it. I tried running on Windows 7 Starter on a netbook (Intel Atom processor) and it was hopelessly slow.
The screenshot below shows the Windows Phone 7 Internet Explorer displaying the MSN site.