xmodmap from system script

[Simon Arthur]

I'm attempting to call xmodmap from a script triggered by udev. I want 
this to be able to  restore my mouse settings every time my mouse is 
plugged in. Unfortunately,  unless I call xmodmap from within an X 
session, I get an error:

# /usr/bin/xmodmap  -display :0 /etc/X11/Xmodmap

No protocol specified
/usr/bin/xmodmap:  unable to open display ':0'

This error shows up both when calling xmodmap from my script and when 
logging in via the console (not X). I have tried various settings of the 
DISPLAY environment variable and the -display option, with no success.

This is on Fedora Core 10.
X.Org X Server 1.5.3
Release Date: 5 November 2008
X Protocol Version 11, Revision 0
Build Operating System: Linux 2.6.18-128.1.6.el5 i686

Any help you could provide would be greatly appreciated.