1. look at the BCS Engineering
review bundle...
2. instead of making reviews availale to the customers, make it only visible to admin -- {if $usertype eq "A"}review input section code{/if}
So -- basically, you get the power of the built-in review module, coupled with the admin power of the BCSE mod, and only visible to admins.
This is the fast, easy, cheap solution. It does not give you the "one page" interface -- but this would mean the admin goes to the product page, then enters the review, then uses the admin to "approve" the review.
This is one way to accomplish this. Of course, it could be custom coded -- considering BCS has already invested considerable time in their review mods, they'd be my first call for a custom mod to the review system.
Hope this helps.
Jeremy
-- I deleted your other post