I don't think you can change any cell based on mouse movement over the cell.
If contains a link means contains a link to a different workbook, then maybe you
could use a userdefined function and conditional formatting to highlight them.
You could have the UDF look for .xls, [, ], and !. If it finds all of these, it
might be a link to another workbook. (But those characters could be used in a
formula that doesn't contain a link, too--so it's not perfect.)
A sample UDF:
Option Explicit
Function HasLink(rng As Range) As Boolean
HasLink = False
If rng(1).HasFormula = False Then
Exit Function
End If
HasLink = CBool((InStr(1, rng(1).Formula, ".xls", vbTextCompare) _
* InStr(1, rng(1).Formula, "[", vbTextCompare) _
* InStr(1, rng(1).Formula, "]", vbTextCompare) _
* InStr(1, rng(1).Formula, "!", vbTextCompare)) > 0)
End Function
Then you could use that formula in the Format|Conditional Formatting formula.
If you're new to macros, you may want to read David McRitchie's intro at:
http://www.mvps.org/dmcritchie/excel/getstarted.htm
=======
Short course:
Open your workbook.
Hit alt-f11 to get to the VBE (where macros/UDF's live)
hit ctrl-R to view the project explorer
Find your workbook.
should look like: VBAProject (yourfilename.xls)
right click on the project name
Insert, then Module
You should see the code window pop up on the right hand side
Paste the code in there.
Now go back to excel.
Into a test cell and type:
=haslink(a1)
If it works, try it in the conditional formatting formula.
