I read a lot of howtos, tips, mailing-lists, forums, about this topic but I alwais got a poor experience in Linux synchronization with a Pocket Pc (Windos CE / Mobile) device.

I don't want to write another one howto for Ubuntu, just consider this text a patch (I assume that synce-pstatus is working with the firewall completly OFF)

Synce and the firewall Firestarter

PROBLEM
A very common problem is the error:

synce-pstatus: Unable to initialize RAPI: An unspecified failure has occurred

99% It is due to the firewall configuration, specially if you use firestarter, isn't enought to open the ports 990 5678 5679, because the ip used is on another one interface

SOLUTION
You have to edit user-post:

chmod +w /etc/firestarter/user-post

with:

#iptables -X
#iptables -t nat -F
#iptables -P INPUT ACCEPT
#iptables -P FORWARD ACCEPT
#iptables -P OUTPUT ACCEPT
iptables -t nat -A POSTROUTING -s 192.168.131.201 -j MASQUERADE

Start Synce on demand

Kernel part
It starts synce-serial-start, when the pocket pc is connected

sudo gedit /etc/udev/rules.d/60-ipaq.rules

with:

# udev rules file for SynCE
BUS!="usb", ACTION!="add", KERNEL!="ttyUSB*", GOTO="synce_rules_end"
# Establish the connection
RUN+="/usr/bin/synce-serial-start"
LABEL="synce_rules_end"

It not finished because in usermode you have to start 'dccm' too
So open gnome-session-properties and add dccm at startup.

sudo /etc/init.d/udev restart

Now synce:/// should work on Nautilus