Networking A Win2000 machine to a Win XP machine

Hi, I've been trying to set up a wired connection between my Windows 2000 machine and an old Windows XP machine I found.

My Windows 2000 machine is currently connected to a wireless network which lets its access the internet... However I also want to network the XP machine to it via a cable (So I can play LANs in my room  ).

I've tried many ways in which to get the two computers to reconise each other but nothing I've done has worked. I set up the correct IP's (I think) which normally works between two 2000 machines, and I have  router inbetween them both! Why aren't they reconising eachother!?

PS: They both reconise there is a LAN connection but can't ping or see eachother

[Moderator]

First off, I don't know where you FOUND the machine, but I can't help but think that someone would dump off a computer somewhere becuase they were having problems with it. (There must be a reason that someone left it). Also, I'm not sure that mixing the operating systems like that is a good idea. That COULD be causing your problems.... Just install XP on the other computer if you can get a hold of an XP disk...

[glb]Flame[/glb]

First check that they are in the same workgroup
What ip addressess have you got on the machines and the router?
What subnet masks?

Here is a link to some useful information about networks:

http://www.rcmillar.netfirms.com/subpages/Links.htm#Networks

Have you tried the networking wizard?
Do you have any firewalls active?
The router could be faulty?

Firstly I'd like to say thanks for the replies!  

@Flame: I didnt just 'find' it in the the street lol... no no no, it was one of my dad's old ones, but he doesnt need it anymore... So I have commendeered it.

As for the different OS's well I dont really want to format my 2000 machine (let alone not having an XP cd) as it has alot of stuff on it, and i only just formatted recently... I also want to keep the XP OS on the other machine, as its usful for playing some of my older games!

@Robertmiller: I have set all the workgroups in the house to HOME. Also the ip addresses being used between the two computers in my room is '172.168.12.X' but i dont know what you mean by the routers IP? Also the subnet mask is '255.255.0.0'.

@Neil: I do have a firewall on both machines but I have them disabled while I tried pinging does nothing it seems :S
Also it seems the networking wizard doesn't work on a 2000 machine (go figure), so that kinda buggered up.
And good idea I'll quickly try switching routers

This may you>http://www.wown.com/articles_tutorials/netgeneral/