You can put any valid sequence of Tcl commands as the parameter for the -command option of a button. So, if I understand your question correctly, you might do something like:
button .b -text <whatever> -command {
toplevel .newWindow
pack [entry .newWindow.e -textvariable bt] -side top
set bt <whatever you want>
}
Is this what you're after?
Bob Rashkin
rrashkin@csc.com