There's something out there called "GooSync", which is a for-pay service, that allows you to sync calendar, tasks, and contacts to/from Google via SyncML.

http://www.goosync.com/

If you just want/need 1 device and 1 calendar, it'll do it for free, though (no contacts). And it's set up around doing phones, not random software clients (though, they do have a means of doing generic SyncML client instructions, so you might be able to fool them).

I just signed up for a short subscription, so I can sync my phone (Nokia E61i).

I hear funambol is also working on a Google sync plugin, which would work with their SyncML servers. Supposedly it'll be delivered around the same time as T-Mobile's G1 (ie. intended to be useful for/with Android devices that need to sync with SyncML services).