XP and VISTA on a long ethernet cable - LAN connection

[Microtech2008]

I have a problem.
I am on BT Broadband and for the last 3 months I have tried all BT Home Hubs including the latest one(black) as I cannot connect to my VISTA PC via an Ethernet cable.
The cable is 20 meters long and it work fine if I connect to any Windows XP systems.
If I plug the cable on a VISTA system it won't work unless I reset the router back to default settings.
Vista's default DHCP server IP address is always 169.254.203.7

I have tried 4 different VISTA computers with exactly the same symptoms. I have contacted Microsoft, explained the issue, tried with them all sorts of things. No results or answers. Is this another VISTA Bug?

[Goblintech]

I have seen this problem on a client's line but I have realized that this is not a vista problem but a Thompson router problem. I have tried another cable and it did the same. I have tried another 2 computers and it did the same. As soon as I changed the router it all connected just perfect. My client's router is a BT Home Hub v2, a branded thompson hardware.
Change your router and see what it does. (let us know please)