Thanks for the suggestions!
@whooami: I had tried it from a Vista machine as well as Windows 7, and from three different browsers. Not sure why it would show up on a Mac but not Windows, since PHP code works through a browser, not a client-side OS, per se.
@shane G: I’ll give that a try. Would reinstalling the wp-includes hose my theme at all? I’ll also try to upgrade to WP 2.8.3.
Thanks guys, I appreciate the help with this. I’ll report back how it went.