These lines I posted have to be copy-pasted in the file /etc/apt/sources.list

/etc/apt/sources.list is not a command!

So first you should install becomeroot.

With this, you will be able to become root ( by typing sudo gainroot in xterm ) and then will be able to edit this file (which is only writeable by root).
2 things:
*As somebody said, TAKE CARE, root has full power on the device. If you do a mistake, get ready for a reflash (happened to me already 3 times in 2 months)

*How will you copy-paste the content or how to overwrite the file...
Ok I've set up a webpage for you:
Grab wget:
http://maemo.org/downloads/product/OS2007/wget
click install

Then
open xterm
Go to the correct directory:
cd /etc/apt
Become root (using becomeroot)
sudo gainroot
Make a backup of your current sources.list:
mv sources.list sources.list-orig
Grab the new sources.list from internet:
wget http://debfarm.free.fr/images/src.txt
Rename it
mv src.txt sources.list
Close xterm

Go in application manager and click on check for updates.
You should have more applications.
This sources.list is far from exhaustive, maybe I'll update the post later.