I should have posted this update earlier but do so now in the hope that it will be of aid to others. Went back home and after a little experimenting found the solution.
select Configure the System
then go to Appearance/Screen/Resolution
left click on your apple remote to select the menu items
for my case (42 inch Phillips Plasma) I found that selecting 1280 x 1080 worked the best but it was not perfect.
Then navigate back to Appearance. Select Look and Feel and then Skin
Left click to select the menu items and set the zoom to either up or down to fit the XBMC screen perfectly on your screen. In my case a setting of -6% worked perfectly.
This is for the Altantis bf1 version.
Works beautifully and much prefer it to the standard AppleTV or even Boxee screen display. Really makes the others look kinda stodgy.
Now on to the task of getting the SMB shares set properly so I can back up the HD’s I have attached to the AppleTV unit.