Hi all.

Is there any software or program on Windows XP or Windows Vista that allows two users on two different PCs that are connected on the same Local Area Network (LAN) to chat with each other. Basically, apart from downloading 3rd party software, I would like to know if there is any way this can be done.

Thanks,
-Anton

Yes
If your running xp you can use the net send command.
Firstly make sure the messenger service is enabled and running on all computers.
Start--run--services.msc
From here search for the messenger service and set it to automatic start.

Now go start--run--cmd
The command you use is

netsend (Computer name) message
To view computer names on the network use the net view command

example.
netsend MYPC Hello, how you doing ?

This only works in XP. I just read that the netsend command got removed from vista and win 7.
In Vista and windows 7 i beleive you can use the msg command. Just type msg into command prompt and it will list you all the available options.
To be honest it's not a great way to talk and there might be better ways of doing so, also i'm not sure if theres any security risks in starting this messenger service.
Oh and of course you need have your basic networking setup correctly to do this

As account73 mentioned there may be security issues. In particular, I'd think
1) you need to make sure your a network firewall (e.g. the one on your network router) blocks all outside traffic to the ports used by Messenger
2) This makes sure only your LAN computers use those ports
3) Otherwise, you may get pop-up messages coming in over the Internet of unknown origin

thanks a mil guys....tried your suggestions and they work fine