Tkinter gui for the winnt subst command

[yuval]

I need to map and remap (cmd.exe subst ...) certain 
directories on my computer very often. Therefore I wrote a 
Tkinter gui which upon button press performs essentially
cmd.exe /c subst ... with various arguments.
I tried several approaches (os.popen, os.system,spawnv) for 
running the command. Unfortunately with all these approaches 
it takes the command a very, very long time (~30 seconds) to complete.
I am running Python 2.1. Does anybody know where the 
problem lies and how to solve it?