First, connect them so that both can interchange data. you can test this by using any services or go to the comand line
(Windows: Start->Run: cmd [enter], Unix/KDE: [alt+f2] konsole [enter], other: please say what u're using)
Do this on both computers and you will see two comand lines. Type
(Windows: ipconfig, Unix: ifconfig)[enter] on both computers and you will see two outputs which state your IP addresses. Presumably, the ones you need will be 192.168.0.* with *=a number.
Now type ping (The other ip) [enter], i.e. ping 192.168.0.1[enter].
You will now see either an error message or some messages including a time, like "4ms". If the output doen't stop (using unix?), Type [Ctrl+C].
If there is an error, please report. Otherwise, your network works.
Now you have to initialize the server, the computer you want to connect to. There is a bunch of methods:
(KDE:) Built-in VNC, server accessible via [Alt+F2]kcontrol[enter]->Internet->Remote Desktop Sharing, client via [Alt+F2]krdc[enter].
VNC: http://www.tightvnc.com/ or http://www.realvnc.com
Install server and client on both computers and start them.
(Windows built-in)
Activate remote desktop sharing here: Start->My Computer->Remote Desktop Sharing.
Press [Win+F1] to access the windows help. Search for a label "invite a friend or expert ..." and follow the assistent. You may select to send an invitation to your client computer.
Double click to this invitation.
Now enter the server's IP address click something like "connect" and you're done. For more information, please specify
1. What system are you using: OS (Like Apple OS X, *BSD, Linux, Windows), version
2. What have you tried so far. Did you install a program?
3. How do you want to use remote desktop sharing? Just one time or more often, what do you want do to with it?