This script should would with every version of tcl/tk from 8.0
to the current, just released 8.5.0

There is nothing wrong with the earlier Tcl version in this
thread. Just wanted to add a little Tk.

Current practice would be to run with tclsh, and a first line
"package require Tk", however, the script as written will
work with older installations. The script could be simpler still,
and utilize only one toplevel widget, but, I kinda like it this way

#! /usr/bin/wish

wm withdraw .
wm title . "Welcome!"

toplevel .t
wm withdraw .t

wm title .t "Sign in Please!"

label .t.l -text "Please enter your name: "
entry .t.e -textvariable name

grid .t.l .t.e

wm deiconify .t

bind .t.e <Return> myproc

proc myproc { } {
wm deiconify .

label .l -text "Welcome to Ubuntu"
label .l2 -textvariable name

button .b -text "Exit" -command {exit}

grid .l .l2
grid .b -columnspan 2
Hope someone finds it interesting.