A working version of Pilot Install for the mac (freeware) has been released that easily lets you install PRCs to your Treo, without going through a full sync (I used the old one all the time, but it expired). This one works with Panther. Very convenient.

http://pdassi.download.de/product.php?prod_id=9378

The site's in German, just click on "Jetzt Downloaded" (What would Goethe think!); the app is in English.

Best,
--Mathew