Ryan R. emailed me the following hint. He explains:
"Internet Explorer 5.2.3 has not been updated in a while, and still retains a skin suited best for Jaguar. A simple update to the Hexadecimal code can give IE for OS X a Panther-like skin (as seen in this screenshot), so that IE no longer has to stick out like a sore thumb. Using an Hexadecimal editor such as HexEdit, open the IE package contents and go to Contents -> MacOS and then open the 'Internet Explorer' file. Go to the Address (command-J using Hexedit) 2FA014 (using the latest version of IE, 5815.1). This is the 18 bytes of code you will want to edit:
EE EE EE EE EE EE E6 E6 E6 E6 E6 E6 EE EE EE EE EE EE FF FF FF FF FF FF
Replace those 18 bytes with:
EE EE EE EE EE EE EE EE EE EE EE EE F3 F3 F3 F3 F3 F3 F3 F3 F3 F3 F3 F3
Save the file then restart Internet Explorer."
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040326072359246