Understanding Alter Source IP

Hi All
Could you help us? We're attempting to understand 'Alter Source IP' in the Advanced Configuration page of GIT because we are exploring it as a solution to getting our Rome Total War games joinable. The evidence that the setup is almost working is that we can see games in the LAN list.
Please could somebody explain how to use the 'Alter Source IP' section of the advanced config page and maybe let us know if we're barking up the right tree?
Many thanks, in advance :)
_______________________
SITE A
game pc 1
laptop(XP sp2) connected to Win2K server (via switch),
- GIT [Client]
internet server
Win2k Server connected to Blueyonder Cable Modem
-ICS (forwarding port 213 TCP to laptop IP)
-ZoneAlarm (permitting TCP 213 in&out)
_______________________
SITE B
broadband router connected to blueyonder cable modem
-NAT forwarding TCP 213
game pc 2
PC (XP sp2) connected to broadband router
- GIT [server]
Could you help us? We're attempting to understand 'Alter Source IP' in the Advanced Configuration page of GIT because we are exploring it as a solution to getting our Rome Total War games joinable. The evidence that the setup is almost working is that we can see games in the LAN list.
Please could somebody explain how to use the 'Alter Source IP' section of the advanced config page and maybe let us know if we're barking up the right tree?
Many thanks, in advance :)
_______________________
SITE A
game pc 1
laptop(XP sp2) connected to Win2K server (via switch),
- GIT [Client]
internet server
Win2k Server connected to Blueyonder Cable Modem
-ICS (forwarding port 213 TCP to laptop IP)
-ZoneAlarm (permitting TCP 213 in&out)
_______________________
SITE B
broadband router connected to blueyonder cable modem
-NAT forwarding TCP 213
game pc 2
PC (XP sp2) connected to broadband router
- GIT [server]