Eureka!

Download and install Steam. Create an account. Sign in.
Download and install Zero Gear Demo ( http://store.steampowered.com/app/18800/)
That might take about half an hour or more.

After Zero Gear Demo is 100% downloaded,
go to the folder containing it, most likely
C:\Program Files\Steam\steamapps\common\zero gear

In here you'll find an icon that says "ZeroGear" and is 1kb(size). Right-click this icon and select "edit".

A notepad file will appear.
erase everything inside and type this instead:

C: cd\
cd Program Files\Activision\Modern Warfare 2
START iw4mp.exe

That may vary depending on where your game is installed in.

Next, download this:
http://www.multiupload.com/NTQPWD0B7O

extract it into the right folder(where your MW2 is installed, typically :
Program Files\Activision\Modern Warfare 2)

Then start the Zero Gear Demo through Steam. Should work like a charm.

*all credit goes to the helpful people on the interwebs. God bless your communistic vision.