This weekend, I found out that my Vista PC would not sync to the share on my iMac. At first, I thought something was wrong with my samba settings (as the iMac was just set up), but after I turned to google, I found that this problem is caused by an error in the OEM version of Vista. A quick registry hack, solves this:

Create the parameters key in the following location :

Then within the parameters key, create a DWORD Value named FormatDatabase with a value of 1 (hex) then reboot the machine.

(found here)