Hi Jeremy, welcome to MrExcel!
You could try something like this, although there may be a better way,
<font face=Courier New><SPAN style="color:#00007F">Option</SPAN> <SPAN style="color:#00007F">Explicit</SPAN>
<SPAN style="color:#00007F">Sub</SPAN> testeroo()
Application.ScreenUpdating = <SPAN style="color:#00007F">False</SPAN>
<SPAN style="color:#00007F">Dim</SPAN> rng <SPAN style="color:#00007F">As</SPAN> Range, _
cel <SPAN style="color:#00007F">As</SPAN> Range
<SPAN style="color:#00007F">Set</SPAN> rng = [A1:A20] <SPAN style="color:#007F00">'change range to suit</SPAN>
<SPAN style="color:#00007F">For</SPAN> <SPAN style="color:#00007F">Each</SPAN> cel <SPAN style="color:#00007F">In</SPAN> rng
<SPAN style="color:#007F00">' the offset will put the zip code in the column</SPAN>
<SPAN style="color:#007F00">' directly to the right of your rng.</SPAN>
cel.Offset(, 1).Value = Right(cel.Value, 5)
cel.Value = Left(cel.Value, Len(cel.Value) - 5)
<SPAN style="color:#00007F">Next</SPAN> cel
Application.ScreenUpdating = <SPAN style="color:#00007F">True</SPAN>
<SPAN style="color:#00007F">End</SPAN> <SPAN style="color:#00007F">Sub</SPAN>
</FONT>