Full Mailbox RIghts of all Users

i want to know why you want to do this , because if i'm understanding the reason right i can tell you another easy way by adding the send as recieve as right to the whole information store for the specific user or group

I want to grant an administrator on the network access to other users mailboxes so that he can monitor other employee's emails. I don't want to give him the receive as permission because I don't want to flood his inbox with over 70 employee's emails. I just want him to be able view other user's mailboxes at his leisure. I can grant him Full Mailbox right to individual mailboxes, but I don't know how to grant to all mailboxes.

Give them rights to to the MailStore in Exchange System Manager.  Click the Mail Store, then Choose Properties, then Security, you can customise the security options to allow whichever permissions you'd like.  You will need to do this to each mail store if you have multiple ones.

the send as recieve as will not affect the mailbox of the user so do it , it will give him the right to monitor

Exchange 2007 does not have exchange sysem manager??  I believe the rights must be  set in Exchange management shell.  i found the command line  but stil  need help.   :
# Grant full mailbox access permission
Add-MailboxPermission testmbx -AccessRights FullAccess -user jaredz

I'm not sure what to replace testmbx with

I solved the issue running below command, it gives full access permission to all the mailboxes .
Get-Mailbox | Add-MailboxPermission -AccessRights Fullaccess -User <Username>

also, if you need to run this command where you have more than one active directory being managed by a single Exchange server, then the syntax should look like this:

Get-Mailbox -DomainController <FQDN of DC> | Add-MailboxPermission -AccessRights Fullaccess -User <Username>