Okay then, make use of the Characters mehtod ..
Sub MakeWordBold()
Dim strSearch As String, searchRng As Range, i As Long, cel As Range
Set searchRng = Range("A1:A10")
strSearch = InputBox("Please enter the text to make bold:", "Bold Text")
If strSearch = "" Then Exit Sub
For Each cel In searchRng
With cel
.Font.Bold = False
For i = 1 To Len(.Text) - Len(strSearch) Step 1
If Mid(.Text, i, Len(strSearch)) = strSearch Then
.Characters(i, Len(strSearch)).Font.Bold = True
End If
Next i
End With
Next cel
End Sub