Since this is a question that is raised frequently, I would like to take this opportunity to explain how it's done.
(This only works with version 1.1.0 or better)

Switching to Michelle:
This couldn't be easier. Simply run Michelle's executable and it asks you whether to use Michelle as the default desktop shell. Answer yes and logout. When you login, you will be using Michelle.

Switching back to Explorer:
I have made some alterations to Michelle's start-up code to aid switching back to Explorer should it go horribly wrong. There are now 2 methods in order to return to Explorer:

1. Right click Michelle's caption bar and select 'Use Explorer', and follow the prompts.
2. Michelle has a command-line switch -e which can be used from Task Manager. Start a new task and browse to Michellle. Simply add -e to the end (e.g. "...My Documents/michelle.exe" -e) and follow the prompts.

Using the 2nd method can be used even if Michelle is already running but unresponsive.

I removed the 'Install' and 'Uninstall' from the caption's right click menu, and replaced them with: 'Use Michelle' and 'Use Explorer'. This was to make it less confusing. After all, Michelle isn't installed at all. It simply changes a few registry settings to point to Michelle instead of Explorer.

If you have any problems with this, or any suggestions, please leave your comments here.