Internet Sharing with ADSL

I have a crossover cable from router to hub Uplink port… I have straight cables from hub to to two Pentium 4 computers with XP Professional…. I can get either computer to go on line. I can’t get both computer to attain an IP address at the same time… Is it something I’m doing wrong or is it an ISP problem….. If I want to go on line with the other computer, I have to use ipconfig /release on the computer I’m on and then use ipconfig /renew on the other computer……… Anybody havean answer for me….