shutdown plugin?

Hi Guys,
I am going to move my wpmu from one host to another. I need a kind of shutdown plugin so that once i backed up my database, i will shutdown the site so no one will be able to post/edit/delete or even login to there account until i move everything on the new hosting and then they can start using the service.

the main point is actually not losing a single data during the migration.

any solution?

by the way the link for WPMU Shutdown Plugin at itdamager.com is not working.

Thanks,
Jamshid