Something

#!/bin/bash
PROG=mythfrontend
STATUS=`ps -e | grep $PROG | grep -v grep | wc -l | awk '{print $1}'`

if [ `echo $DISPLAY | grep -c ":0"` -ge 1 ]
then
    if [ $STATUS -eq 0 ]
    then
        ( $PROG & )
    else
        killall $PROG
    fi
fi
exit 0