Sure. Here's a example testing for Date:
<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> IsDate(rng) <SPAN style="color:#00007F">Then</SPAN> rng.Interior.ColorIndex = 3
<SPAN style="color:#00007F">End</SPAN> <SPAN style="color:#00007F">Sub</SPAN></FONT>
HTH,
Smitty