Here are 3 different methods to center a job (assuming you have already loaded in the gerbers):
SUGGESTION #1: USING SET ORIGIN. Many jobs have a centered object such as a "fiducial" or "border" that can be used to easily find the center. (A) If there is a "fiducial" or centered object, set object snap to "Auto" (menu: View | Snap | Auto (cen+end)), and then goto "Set Origin" (menu: Setup | Set Origin) and select that object. The 0,0 coordinate will now be placed in the center of the board.
(B) If there is a "continuous" border (i.e. you click on the border and it is one object - not separate segments), then set object snap to "Object-Center" (menu: View | Snap | Object-Center), and then goto "Set Origin" (menu: Setup | Set Origin) and select the border edge. The 0,0 coordinate will now be placed in the center of the board.
Note: If you're border edge is "not continuous" (i.e. separate segments), you can always use the Join feature to combine those segments into one border object.
SUGGESTION #2: USING MOVE. If you know where the offset to the center is, then using the move is a great idea. Select All objects (menu: Edit | Selection | All), then activate "move" (menu: Edit | Move), type in your "Base Point" (into the command window at the bottom) you can make this the center offset point, and then choose your "Second Point of Displacement" this will be 0,0
SUGGESTION #3: USING JOB INSERT. FAB 3000 supports hierarchy so it's easy to center an entire job - here's how. Create a "New Job" (menu: File | New | Job...), Now lets insert the previous job (menu: Job | Insert Job...) a dialog will now appear; in the bottom right corner change the "Job Anchor Point" to "Center" and press OK. In the command bar it asks for the "Origin point" so enter in 0,0. You now have the entire job centered.
There are probably many other ways you can use FAB 3000 to center objects including writing a custom scripts to automatically do this for you after import. Most customers choose FAB 3000 because there are many more editing features available than your standard CAM software.