I'm just posting a follow up that I thought would be helpful.
I'm not trying to bump the thread or anything (hey, my problem's resolved).
After I discovered that the codexsearch.php plugin was the culprit and removed it, I looked at my php log (shoulda looked sooner) and it had multiple entries like this:
"[13-Jun-2006 03:46:24] PHP Warning: Cannot modify header information - headers already sent by (output started at /big/dom/x[domain]/www/blog/wp-content/plugins/codexsearch.php:2) in /big/dom/x[domain]/www/blog/wp-rss2.php on line 8
&
[13-Jun-2006 19:40:11] PHP Warning: Cannot modify header information - headers already sent by (output started at /big/dom/x[domain]/www/blog/wp-content/plugins/codexsearch.php:2) in /big/dom/x[domain]/www/blog/wp-includes/pluggable-functions.php on line 325"
So the php log was very specific and helpful, which most of you probably already know.
Also, since I've tried about 15 different themes and none of them crashed my dash, I'll editorialize that in my experience plugins are especially risky to install. Some have had problems with themes, but not me.
Cheers,
Myra