You can do this with data validation but there are limits as to how much
"protection" this will give you. You can try this out and see if it meets
your needs.

Create this defined name:

Goto Insert>Name>Define
Name: SH1C3
Refers to: =Sheet1!$C$3
OK

Select the range Sheet2 C3:C10
Goto Data>Validation
Alow: Custom
Formula: =SH1C3=""
Uncheck Ignore blank
OK

Users can not ENTER (type) data into Sheet2 C3:C10 unless Sheet1 C3 is
empty. They can, however, drag and drop, cut/paste, copy to or delete.

Biff