first do a save-as to a new filename.
you need to close the schematic editor if you are using it.
then you run the "panelize.ulp" (user language program). this copies everything on the tNames and bNames layers to new layers called _tNames and _bNames. reason being, Eagle automatically keeps track of stuff on the tNames, bNames layers and you will end up with different component lables for the same part on each pcb of the panel. ie J1 will turn into J2 when you copy it. Eagle doesnt keep track of _tNames, so you can essentially have two components with the same name on one layout.
now turn off tNames and bNames.
copy and paste you layout as desired. ..that is a procedure in itself! I posted that question here a while back and someone explained it, do a search.
mike p