Welcome to the Board!
You can use the Open event with a test to see if the date's already there:
<font face=Tahoma><SPAN style="color:#00007F">Private</SPAN> <SPAN style="color:#00007F">Sub</SPAN> Workbook_Open()
<SPAN style="color:#00007F">Dim</SPAN> rng <SPAN style="color:#00007F">As</SPAN> Range
<SPAN style="color:#00007F">Set</SPAN> rng = Sheets("Sheet1").Range("A1")
<SPAN style="color:#00007F">If</SPAN> LenB(rng) = 0 <SPAN style="color:#00007F">Then</SPAN> rng = <SPAN style="color:#00007F">Date</SPAN>
<SPAN style="color:#00007F">End</SPAN> <SPAN style="color:#00007F">Sub</SPAN></FONT>
Hope that helps,
Smitty