Simply scroll to the table below and click on the username (last column) to connect to that server. If it says "Unable to connect to host" it's most likely that your internet connection is broken or that the server is not running. If it gives any other message (but does not connect) you are probably too far away from the host or there are other problems with the connection.
Doing this is COMPLETELY VAC2 safe and you WILL NOT get banned for this.

You will need to follow some more steps before you do this:
1. Download MW2 Liberation v1.04 (for donor-functions take a look at YouTube: MW2 Liberation v1.04 Donor-Unlock )
2. Download LobbyTracker
3. (optional) Download some mods to host (Search on MPCForum, MPGH or Se7enSins)
4. Create an account on http://www.itshax.com/LobbyTracker/register.php
5. Run LobbyTracker and login there. It should say "Waiting..."
6. Run Call of Duty: Modern Warfare 2 with MW2 Liberation
7. LobbyTracker *should* say "Ready". Don't close the program now because it stops keeping your lobby on the list as soon as you close it.
Actually this also works without MW2 Liberation, but since hosting games with Mods (not joining!) is VAC2 detected and most people come here for this being modded games it's highly recommended to use a tool like MW2 Liberation to disable VAC2.