'if you are using buttons then
private sub command1_click()
 if command1.caption="" then
  if x then
   command1.caption="x"
  else
   command1.caption="o"
  end if
 end if
end sub

Windows Form Designer Blah Blah Goes Here
Dim ttt(2, 2) As Char 'this is a global vari
    Sub button_handling(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click, Button2.Click, Button3.Click, Button4.Click, Button5.Click, Button6.Click, Button7.Click, Button8.Click, Button9.Click
        Dim temp As Button = sender 'basically creates a copy of the button clicked
        Static chrplayer As Char = "x"
        If temp.Text <> Nothing Then 'if button has already been selected
            Exit Sub
        End If
        temp.Text = chrplayer
        Dim index As String
        index = temp.Tag 'gets which button was clicked. Remember, First Row First Button
'is 00, First Row Second Button is 01, so this is an effective way to get which
'button was clicked in a numerical form.
        Dim intx As Integer = Val(index.Chars(0))
        Dim inty As Integer = Val(index.Chars(1))
        storemove(intx, inty, chrplayer, ttt)
        If iswinner(ttt) = "x" Then
            MessageBox.Show("Winner!")
            lblx.Text = lblx.Text + 1
            newgame()
            Exit Sub
        ElseIf iswinner(ttt) = "o" Then
            MessageBox.Show("Winner!")
            lblo.Text = lblo.Text + 1
            newgame()
            Exit Sub
        Else
            isfull(ttt)
            If chrplayer = "x" Then
                chrplayer = "o"
            Else
                chrplayer = "x"
            End If
        End If
    End Sub
    Sub storemove(ByVal intX As Integer, ByVal intY As Integer, ByVal chrPlayer As Char, ByRef ttt(,) As Char)
        ttt(intX, intY) = chrPlayer
    End Sub
    Function isfull(ByVal ttt(,) As Char) As Boolean
        If ttt(0, 0) <> Nothing And ttt(0, 1) <> Nothing And ttt(0, 2) <> Nothing And ttt(1, 0) <> Nothing And ttt(1, 1) <> Nothing And ttt(1, 2) <> Nothing And ttt(2, 0) <> Nothing And ttt(2, 1) <> Nothing And ttt(2, 2) <> Nothing Then
'probably inefficent, but it works.
            MsgBox("Tie!")
            lblcat.Text = lblcat.Text + 1
            newgame()
        End If
    End Function
    Sub newgame()
        Button1.Text = Nothing
        Button2.Text = Nothing
        Button3.Text = Nothing
        Button4.Text = Nothing
        Button5.Text = Nothing
        Button6.Text = Nothing
        Button7.Text = Nothing
        Button8.Text = Nothing
        Button9.Text = Nothing
        Dim a As Integer
        For a = 0 To 2
            ttt(a, 0) = ""
            ttt(a, 1) = ""
            ttt(a, 2) = ""
        Next a
    End Sub
    Function iswinner(ByRef ttt(,) As Char) As Char
        If ttt(0, 0) = "x" And ttt(1, 1) = "x" And ttt(2, 2) = "x" Then
            Return "x"
        End If
        If ttt(0, 0) = "o" And ttt(1, 1) = "o" And ttt(2, 2) = "o" Then
            Return "o"
        End If
        If ttt(0, 0) = "x" And ttt(0, 1) = "x" And ttt(0, 2) = "x" Then
            Return "x"
        End If
        If ttt(0, 0) = "o" And ttt(0, 1) = "o" And ttt(0, 2) = "o" Then
            Return "o"
        End If
        If ttt(1, 0) = "x" And ttt(1, 1) = "x" And ttt(1, 2) = "x" Then
            Return "x"
        End If
        If ttt(1, 0) = "o" And ttt(1, 1) = "o" And ttt(1, 2) = "o" Then
            Return "o"
        End If
        If ttt(2, 0) = "x" And ttt(2, 1) = "x" And ttt(2, 2) = "x" Then
            Return "x"
        End If
        If ttt(2, 0) = "o" And ttt(2, 1) = "o" And ttt(2, 2) = "o" Then
            Return "o"
        End If
        If ttt(2, 0) = "x" And ttt(1, 1) = "x" And ttt(0, 2) = "x" Then
            Return "x"
        End If
        If ttt(2, 0) = "o" And ttt(1, 1) = "o" And ttt(0, 2) = "o" Then
            Return "o"
        End If
        If ttt(0, 0) = "x" And ttt(1, 0) = "x" And ttt(2, 0) = "x" Then
            Return "x"
        End If
        If ttt(0, 0) = "o" And ttt(1, 0) = "o" And ttt(2, 0) = "o" Then
            Return "o"
        End If
        If ttt(0, 1) = "x" And ttt(1, 1) = "x" And ttt(2, 1) = "x" Then
            Return "x"
        End If
        If ttt(0, 1) = "o" And ttt(1, 1) = "o" And ttt(2, 1) = "o" Then
            Return "o"
        End If
        If ttt(0, 2) = "x" And ttt(1, 2) = "x" And ttt(2, 2) = "x" Then
            Return "x"
        End If
        If ttt(0, 2) = "o" And ttt(1, 2) = "o" And ttt(2, 2) = "o" Then
            Return "o"
        End If
    End Function