This is trivial, I know, but it might help someone out there that might have this issue.

I have rebuilt my web server box finally (having lost the domain controller several weeks ago due to a hard drive crash).  I had backed up all of my databases and now needed to restore them onto my newly reinstalled box.  This time, I decided to use my SQL Server 2005 Standard rather than my previous SQL Server 2000 (but that doesn't really have anything to do with this).

I don't like to put my databases in the standard SQL Server location (e.g. DRIVE:\Program Files\Microsoft SQL Server\MSSQL\Data).  Instead, I place them in a completely different file tree mostly for consolidation purposes, not to mention that it makes management easier to not have files scattered all over.

Additionally, as I install SQL Server, I don't like to have the various support services run under LocalSystem or Administrator, but rather create a low-privilege account.

When you go to restore a database .BAK file, you are presented with a directory tree of the server.  You then need to navigate to the location of the .BAK file to select it.  Despite the fact that you might be logged into SQL Server as Administrator or anyone high-level account, it will browse the directory tree under the user credentials that you specify for the MSSQLSERVER service - NOT the account with which you're logged in.  Therefore, you need to grant that user appropriate permissions in the database directories (both the destination folder as well as the backup folder).

Once you do that, you should be all set!