WinXP PtoP network and Outlook

Hi all. Hopefully somebody can help… 🙂
I have 3 PCs w/WinXP Home on each, networked into peer-to-peer network, one box(which is main) is using Earthlink DSL as an internet conection, shares it with others on the network. Here is my problem: all PCs can access the Internet using that DSL conection on main PC, main PC’s
Outlook works too, but I can not find how to make Outlook Express 6 on other 2 PCs to use that shared DSL connection….? Can anybody point me into right direction, please?