Locking Cells when user inputs data
 

I am using Excel 2007 and I am trying to figure out how to "lock" a cell so
that when I import data in as a table, the import will not overwrite the
cell.

Also is it possible at the same time to have excel analyze the incoming data
and to determine if the incoming numbers are LOWER than the numbers inputed
by the user into the "locked" cells?

Lastly, I plan on using the color green for the user inputed data and so if
this helps with coding or creates any problems I just wanted to let everyone
know.

Thanks!