I had already downloaded and installed Flash for Firefox, following these instructions but could not get it to work as a plugin on Chromium.

Success is yours when you type "about:plugins" into the location bar of Chromium and the Flash player appears.

Fortunately, it turned out to be pretty simple to just link Firefox's plugin into Chromium: As root, do this:

cd /usr/lib64/chromium-browser/plugins/
ln -s /usr/lib64/mozilla/plugins-wrapped/nswrapper_32_64.libflashplayer.so .

1) Add the backports repository by editing /etc/apt/sources.lst (must be root) and adding the following line:

deb http://www.backports.org/debian/ lenny-backports main contrib non-free

Run the following:

#aptitude update
#aptitude install debian-backports-keyring

(Ignore any warning that occur with the above 2 commands, the install will correct those) If you run #aptitude update again the warnings should be gone

2) Install Adobe Flash

#aptitude install flashplugin-nonfree

3)You shouldn't need this step, but just in case run

and make sure the correct one (/usr/lib/flashplugin-nonfree/libflashplayer.so) is selected. It should be the current default.

4) Start Iceweasel and go the location about:plugins and you should see the latest Flash.