still too hard even with the code given by stephan.. your really need GIS to do this...I feel and idea brewing....
you might be able to use excel to create equations that if object A has coordiantes x1,y1 then it lives in A6
so you use the export coordiantes tool to export the coordiantes of all your cells 1 type at a time as it cant tell them apart ( or use the vba code from stephen) then use excel to create your formula basically pythagoras to check as each grid square has an upper x,y and lower x,y so you could build if statements or lookup tables that take an imported coordiante and return the grid square name that fits in the range of coordinates... much easier than vba..
but if you move any cells you have to re run the extract and put into your excel formulaes...
sounds like a great little project challenge...