You could try dis-abling the Net Send command in the MS-DOS prompt
you could.. but it is easier to follow the NSA info you will find that Messenger (NetSend) will be included in this pile..

www.blackviper.com will be a good resource for disabling un-need services like messenger..

the crux of this thread goes way beyond the services like messenger.. and for goodness sake ..don't confuse it with MSN Messenger (which will probably be pissed off as well)

untuchable-me's post was interesting read.. thanks for that

Cheers

By the way I don't know why people are calling the 2k/xp CMD prompt MS-Dos? why? it is the Command prompt.. there is no DOS in XP or 2k.. try running a dos app in xp/2k without a DOS emu and see how ya go