If I recall correctly, there was once a version of BackTrack (1 and 2, I think. Maybe even 3) that you could easily start X with either fluxbox or KDE by typing 'flux' or 'kde'.
(Or maybe it was 'flux' and 'startx')
At any rate, I just installed BT4, R2 which comes with fluxbox again, and created myself two new scripts - /usr/bin/flux and /usr/bin/kde - since I sometimes want to run in one or the other.
Note: running startx will simply launch wichever desktop manager you used last. :)
Attached is a script that installs both of those scripts for you, or you can cut and paste code to create them manually, yourself.
The above is also available here: http://pastie.org/pastes/1363907/tex...detyjbwbzxnska
echo "This will create two scripts: /usr/bin/flux and /usr/bin/kde";
echo "Continue [Y/n]?"; read choice;
if [ "$choice" == "n" ];
echo "#!/bin/bash" > /usr/bin/flux;
echo "echo \"/usr/bin/startfluxbox\" > \$HOME/.xinitrc;" >> /usr/bin/flux;
echo "startx;" >> /usr/bin/flux
chmod 770 /usr/bin/flux;
echo "Created /usr/bin/flux"
echo "#!/bin/bash" > /usr/bin/kde;
echo "echo \"/usr/bin/startkde\" > \$HOME/.xinitrc;" >> /usr/bin/kde;
echo "startx;" >> /usr/bin/kde
chmod 770 /usr/bin/kde;
echo "Created /usr/bin/kde"
echo "Now when you want to run fluxbox, type \`flux\`"
echo "When you want to run kde, type \`kde\`"
and as the attachment below.