Ok, let me attempt to provide some help here as I understoor what David_ross was saying.
1. Make sure that the IP address of the machine running Mandrake and sharing the ADSL connection are the same under both Operating Systems. If for instance your IP on Windows is 192.168.1.1, make sure it is that under mandrake as well.
What the user ment by there can be no conflict with IP is that you are only in one of the Operating Systems at any given time therefore that IP, 192.168.1.1, can not be in conflict.
2. If u are already sharing the ADSL connection between these 3 PCs at home, you are obviously using either "Internet Connection Sharing" or a third-party Proxy, NAT, Gateway. Linux comes with a powerful little tool called IPTables, which in its simplist form can share the ADSL connection with the rest of your home network. Check out
http://www.iptables.org/ for more info on how to get that set up
Hey, if all else fails then just come back to the forum and ask more questions... That is what it is here for after all.
Good Luck.
Nemesis(ZA)