Wow. Might I suggest an alternate way of doing it?
How about something simpler like putting an msnbot.txt file into the root of the domain. Messing around with the robots.txt file may have other robot code suggestions. I would rather not have another standards war over the robots.txt file, if you know what I mean.
This will also give you the opportunity to basicly add more in the future if you wish without disrupting this file.