Network assigning same IP address to two computers

I have two computers connected to a Linksys Etherfast Hub and my DSL modem attatched to that and both computers keep assigning themselves the same IP address from DHCP. Then they both display the "There is an IP address conflict with another computer on the network." This is a problem, obivously, because neither can then connect to the internet or each other like that. Sometimes though, one will connect and the other wont get an IP address. I've done the whole release/renew and they either both get the same IP or one fails and the other is successful.

When I connect just one computer to the hub or straight to the modem, it correctly gets IP/DNS and such and connects to the internet just fine. I bought a new Switch to replace the hub but it has the same problem. Which leads me to believe it is one or both computers that are the culprits. One is a computer I built a few years ago and the other is a week old Compaq. Both are running Windows XP Pro SP2. I have not manually assigned an IP address.

Any ideas?

right click on network icon
left click on properties
right click on connection
left click properties
scroll dwn to tcp/ip highligt
click properties add the ip settings
from your router status window you will get info of your wan
and dsn settings
your default router address
my setup
192.168.1.1 default
192.168.1.129 nic card
mask 255.255.255.0
dns is what you ip gives you
do the same for other nic change 192.168.1. 101 to 225 not the same # as other nic hit OK

Or you could simply look up your modem's settings & see if it's DHCP "server" is configured to assign more then one IP. Maybe you just need to raise the available IPs.

Does that modem work as a router at all? You need a router to share your internet connection.

My Bad should have read that slower
hub's and switchs cannot be used for networking..
you can however make 1 pc a router you will need another nic card.
I am in the process of tweaking dual nics and there is info out there that uses 2 pc's with 1 IP address for both machines however the switch has to be able to do 803.3ad link aggregation and or 803.1Q . also handle ALB.
I am finding out fast only high end switchs do this.
it still may be possable to have connection ,but it will be a little slower
microsoft has link to IT section that discuss's all solutions.
your fix get a cheap 4 port router put the hub aside