Mira, sólo tienes que poner esto en el evento Change del TextBox
Código:
Private Sub Text1_Change()
Dim sCampo As String
sCampo = Combo1.Text
With Adodc1
.RecordSource = "SELECT * from Tabla WHERE " & sCampo & " LIKE'" & Text1 & "%'"
.Refresh
End With
Set DataGrid1.DataSource = Adodc1
End Sub
