You shouldn't need to do anything VPN-wise to get this working, as the 501 will build a tunnel from it's outside interface to the remote networks automatically. If you add the command:
> logging host outside
then that should be all you need.
The error you're seeing looks like a routing problem, do you have a static route in the PIX for the whoel 10.0.0.0 network pointing inside? Or do you have a static command referencing the 10 network that tells the PIX this network is on the inside? Try adding a specific route for the remote 10 network (the one the syslog server is on) and point it out the outside interface.