If you're interested in exploring the Windows Phone 7 Series emulator but don't really want to bother with the entire development environment, we've found a way to do that.
The emulator .exe file will need a few changes to the command line parameters to run independent of Visual Studio. You will still need to download the Developer's Tools for Windows Phone 7 Series but Redmond Pie lays out the three step process to add this string, xde.exe C:\Program Files\Microsoft SDKs\WindowsPhone\v7.0\Emulation\Images\WM70C1.bin, to the command prompt for the the XDE.exe file. This will allow the Emulator to launch without the need to go through Visual Studio.
Nervous about tinkering with the command parameters? Redmond Pie also provides a shortcut for your desktop that will take care of it for you which you can find here.
I did experience one quirk in using the desktop shortcut. I kept receiving an error message that the .bin file couldn't be found. We discovered (or should I say Tim discovered) that the target properties of the shortcut needed a slight modification. If you get a similar error, simply right click on the desktop icon, open up the properties and replace the existing target field with the following (including the quotations) to get the emulator to launch:
"C:\Program Files\Microsoft XDE\1.0\XDE.exe" "C:\Program Files\Microsoft SDKs\WindowsPhone\v7.0\Emulation\Images\WM70C1.bin"
Once launched, you will see the Windows Phone appear with a tool bar to the upper right of the phone. I'm sure the load times will vary depending on your computer but don't be surprised if it takes a few seconds for the WP7S ROM to load. Keep in mind that this is a work in progress and it's entirely possible that you'll run into a few bugs and glitches along the way.
Also, if you want to tinker with the unlocked WP7S ROM, you can find it here, courtesy of XDA Developers. Simply follow the directions to replace the development ROM .bin file and you can explore the unlocked world of WP7S.