Someting I did to customize my site caused it to load improperly. I've reverted to the original template and will make changes one by one until it is corrected. Thanks to Kevin Baker for confirming that I was not the only one seeing the problem. It doesn't show up at work on Windows 2000, only at home on XP.
Update: The problem was with the SiteMeter code. It wanted to be in the main body, not the sidebar. Here is my original post about this problem. Note the date. I've been living with this since 22 June. Urg.