add the code below to the top of your skins globaltemplate. It will stop all but admins from using right click.
acp > Look & Feel > Manage Skin Sets & Templates > Manage TemplatesGlobal Templates > globaltemplate
<if test="!in_array($this->memberData['member_group_id'],array(4,6))">
<script language=JavaScript>
var message="Right click is unavailable on the website!";
function clickIE(){
if (event.button==2){
alert(message);
return false;
}
}
function clickNS(e){
if (document.layers||document.getElementById&&!document.all){
if (e.which==2||e.which==3){
alert(message);
return false;
}
}
}
if (document.layers){
document.captureEvents(Event.MOUSEDOWN);
document.onmousedown=clickNS;
}
else if (document.all&&!document.getElementById){
document.onmousedown=clickIE;
}
document.oncontextmenu=new Function("alert(message);return false")
</script>
</if>
Or if you don't want to show a message change this line
document.oncontextmenu=new Function("alert(message);return false")
to this
document.oncontextmenu=new Function("return false")