After leaving Eudora behind for Mail.app, I keep finding features I miss -- in this case, Eudora's ability to read the "From:" header as mail comes in. I had it set in some filters to give me an audio heads-up when certain folks sent mail.
As far as I can tell, this isn't available in Mail.app, but a workaround is possible using AppleScript using the basic text-to-speech script.
on runSave and run this AppleScript to create the sound file.
set theText to "You've got mail from yo momma."
say theText using "Victoria" saving to "YoMomma.aiff"
end run
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020923060651350