Puoi anke fare cosi'

codice:
Function CercaStringa ( byVal Stringa As String ) As Boolean

DIM Index as Integer
DIM Flag as Boolean

Index =0
Flag = False
while Index <= len(Stringa) And Flag = False

Index = index + 1
if mid(Stringa,Index,1) = "carattere da cercare" Then Flag = True

wend

CercaStringa = Flag

End Function