For me [upgrade 4.0.3810 which I installed about [jan 5, 2009]]
fixed palm syncing as mentioned on [01-27-2009] above.
On jan 23, 2009 my parallels4.0.3810 dowloaded some patch initiated by itself
and now the 'about' panel mentions version 4.0.3810 (23 januari, 2009).
The version numer is still 3810 though, I have no idea what the patch contained.
The 23-jan-patch seems to make no difference for my Palm syncing, syncing still works:
1. initiate 'sync' on palm(USB),
2. click OK on parallels popup (the popup asking to cancel and to sync again),
3. click cancel on palm while it is still trying to sync,
4. click again the sync icon on the palm -> now syncing works
One difference might be that you're on XP (i suppose from your former post) and that I'm on w2k
Another possible difference might be that I set my parallels configuration
for the palm-USB-device to automatically connect to the virtual machine
(not to the mac host).