DouKaku?

# coding: shift_jis

import Tkinter as Tk

root = Tk.Tk()
root.title(u"こんにちは、GUI！")

w = 400
h = 300

root.geometry("%dx%d+%d+%d" % (w, h,
    (root.winfo_screenwidth()  - w) / 2,
    (root.winfo_screenheight() - h) / 2))

root.mainloop()