Dim frm1 As New Form1, frm2 As New Form2 
frm1.TextBox.Text = frm2.TextBox.Text

Public Class Form2
    Public Property TextBox_Text_Property as string
        Get
            return me.Textbox.Text
        End Get
        Set(Value as string)
            me.TextBox.Text = Value
        End Set
    End Property
 
    ...
 
End Class
 
'''aufruf
 
Dim frm as new Form2
frm.TextBox_Text_Property = me.Textbox.Text
if frm.ShowDialog = DialogResult.Ok then
    me.TextBox.Text = frm.TextBox_Text_Property
End if