Thanks for the responses. I like the idea of sharing via ldap - I might just go looking for one of those utilities of which you speak, Pengu. Unfortunately I've never got into coding so the idea of editing the code is out.
Glad to know that I'm not the only one looking for it - anyone with a palm device wants to be able to synch address books with their mail client. I've got thunderbird on my work PC and iBook and am about to put it on my blue and white G3 at home and I'd like to be able to use my palm to provide address book consistency. I've found some sites that talk about Thunderbird's ability to synch with palm devices, but that only seems to be on previous releases (prior to version 1.0). Hopefully the next build will both synch with Address Book and palm devices. The PC is a whole other problem I can do nothing about until a new version of Thunderbird is released. No way I'm going back to Outlook though!