I can’t setup my ?nternet connection

i have two computers in my home. i installed Winxp on the first computer. the other is old so i installed win98 on that. i have an ADSL modem an ADSL internet connection on winXP, when i connect two computers the ADSL connection ip changes and i can’t connect to internet on the first computer.

actually i want to connect internet both of computers. if i don’t connect computers there is no problem.

how can i solve this problem.

i want to use internet in two computers, help me please!

first question: how can i setup the connection for two computers.
second question: how can i block ip changes