If you are getting a 408 error from x-lite this means you are not receiving any response from the sip registration server that you are attempting to connect to with x-lite. There are a number of reasons for this but they could be caused by:
A) Your SIP Settings
b) Your firewall
d) Your router
Try disabling any firewall software you have running on
your desktop, including Windows Firewall.
You can also try connected directly to your cable/DSL modem and bypass your router to determine if the router is causing this problem.