There is an issue with the My Movies 4 installation packages with respects to SQL which is not going to be addressed. That being said, I've been able to roll back from My Movies 5 to My Movies 4 successfully. I've also been able to roll back from My Movies 4.07 to My Movies 4.04. Posted the below over at the My Movies forums outlining the steps required. Enjoy!
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I completely wiped out my Windows 7 64-bit installation of My Movies and SQL not too long ago and was able to successfully install My Movies 4 which uses SQL 2005. The steps I took are outlined below.

1. Uninstall My Movies from Programs and Features.
2. Uninstall all instances of SQL from Programs and Features.
3. Run the My Movies Clean Tool found here.
4. Delete any My Movies and SQL directories left behind.
5. Download Microsoft SQL Server 2005 Express Edition (SQLEXPR.EXE) and rename the file, "SQLEXPR32.EXE".

(When attempting to install My Movies 4 prior to this SQL would fail to download and install. Checking the "C:\ProgramData\MyMovies" directory created by the installer I found a file 0kb in size named, "SQLEXPR32.EXE".)

6. Run the My Movies 4 installation file. When prompted to select the type of installation first place the "SQLEXPR32.EXE" file in the "C:\ProgramData\MyMovies" directory the installer created.
7. Select the type of installation (stand-alone in my case) and next. The installer should then show that it's attempting to install SQL, a separate dialog box being displayed asking if it can run the "SQLEXPR32.EXE" file. Select the option to run the file.
8. After a time you should receive another separate dialog box asking if you're sure you want to install SQL and that if you do "Microsoft SQL Server 2005 Service Pack 3" should be installed afterwards. I selected the option to continue with the SQL installation. (I did not find the service pack was required.)
9. After a few minutes the My Movies installer should notify you that the required components for My Movies have been installed, the option then given to install the actual My Movies application.
10. Continue with the My Movies installation at that point which should complete successfully.
11. Once installed launch the Collection Management application which should connect to the My Movies database instance without issue prompting you to log in to your account.