You're quite welcome. You Text3 value is actually the reversing of pairs, not a simple reverse of the string. Try this:
'This assumes Text1 will always be 18 characters long. Test for it or pad it to 18 characters.
Dim tmp As String
Text1.Text = "80ad0120327405c1d8"
'Last 8 characters
Text2.Text = Right$(Text1.Text, 8)
'Simple reverse of the 8 character string
Text3.Text = StrReverse(Text2.Text)
'Revering pairs of the 8 characters
For j = 9 To 1 Step -2
tmp$ = tmp$ & Mid$(Text2.Text, j, 2)
Next
Text4.Text = tmp$