Here's my attempt at finding the two cell addresses.
There's not a lot of logic here. It just looks at the characters following
the "!" Character.
There may be a better technique. I shortened the string a little.

Returns:

Found: 2
$U$77
$U$85

Sub Demo()
'// = = = = = = = = = =
'// Microsoft VbScript Regular Expressions 5.5
'// = = = = = = = = = =

Dim Re As RegExp
Dim MyEquation As String
Dim AllPositions As MatchCollection
Dim Position As Match

'// Looking for a cell Address:
Const LookFor As String = "![$ 0-9 A-Z]+"

MyEquation = "'P:\[Book.xls]Allo'!$U$77*10-'P:\DMB\[Book.xls]Allo'!$U$85"

Set Re = New RegExp
Re.Pattern = LookFor
Re.IgnoreCase = True
Re.Global = True

If Not Re.Test(MyEquation) Then Exit Sub
Set AllPositions = Re.Execute(MyEquation)
Debug.Print "Found: " & AllPositions.Count

For Each Position In AllPositions ' 0-Indexed
Debug.Print Mid$(Position.Value, 2)
Next Position
End Sub

--
HTH :)
Dana DeLouis
Windows XP & Office 2007

<snip