I use openbox with KDM and I have a problem. I have a logitech mouse ( MX518 ) that I need to shift the buttons on in X in order to use the next, previous buttons on its side.

I have made changes to xorg.cong:
Option "Buttons" "10" # adding this enables the extra buttons on the MX510
Option "ZAxisMapping" "9 10" # adding this maps wheel scrolling events to mouse buttons 9 & 10
but I need to remap the buttons using xmodmap. (xmodmap -e "pointer = 1 2 3 6 7 8 9 10 4 5") So far I have made the needed changes in ~/.xmodmap and called this from .xsession (even made a link to .Xsession just in case) with no luck. I have looked at /etc/X11/Xsession which should call this file, but the system doesn't seem to call it, in addition I have located a similar file in /etc/kde3/kdm/ which I have tried editing to show a log that it has been called, similarly with no luck.

How is the login flow in KDM? How can I change the login flow so that my local .xsession is called by the system?