xp workgroup problem!!!!!!!!

Hi guys,
i am trying to workgroup my two xp machines. when i set the ip addresses to be obtained manually the can both talk and ping each other perfectly but this knocks off the broadband which needs an automaticly obtained ip address. When i leave them automatic they cannot communicate. When i finally network these two machines i shall use ics for the second pc to access the internet.
i have both pcs plugging into an ethernet box and the modem.

any help would be wicked
chhers