You can create an offline Exchange server to handle this, but this takes time and diligence; however, it’s the safest way to do it. You would create a duplicate domain (dcs only), Exchange Server, and backup server to resotre the data. You can then connect a client PC to pull the data off. To do this, you need to make sure your domain is named the same, the same major service pack is on the DC, you need to setup the Exchange server with the same org name and hostname, and your ervice pack is the same on Exchange. You can take the already restored data back on once you run isinteg on it.
We just did this last week to restore a Public Folder. We don’t use MSBackup for our backup system, but if you take this route for your restore, it won’t matter. As long as you have the priv.edb and oriv.stm files, you should be good.
The unsafe way to do it is to restore over what you have, but that will wipe out anything new after the restore date. I don’t think you can pick andb choose which email box to restore with MSBackup. You really should convince your manager to buy a better backup product that will allow you to restore individual mailboxes.