Getting Netflix to work on my original AppleTV w/ ATV Flash was quite easy. This was done using my Mac Book Air and Cyberduck (FTP). I already have Adobe Flash and Firefox installed and working on my legacy AppleTV.
1. Download and install this on the computer http://silverlight.dlservice.microsoft.com/download/b/c/9/bc9158df-e292-4afe-92c2-2935e7ee61db/81005/Silverlight.2.0.dmg
2. Once Silverlight is installed on the computer open up the Finder or click on the HD icon on the desktop. In the root directory of your HD there's a folder called "Library", click on that. Now, in the "Library folder" there's a folder called "Internet Plug-ins". Click on the "Internet Plug-ins" folder and scroll down to the file named "Silverlight.plugin". We're going to use Cyberduck (FTP Program) to copy that file to the AppleTV.
3. Start your FTP program and connect to the AppleTV. You should see a directory structure in the FTP program window. Open the Folder called "Library" and find the Folder called "Internet plug-ins". Open the "Internet Plug-ins" directory. Now drag the file named "silverlight.plugin" from the computer and drop it into the "Internet plug-ins" directory on the AppleTV. Now, check the "internet plug-ins" directory on the AppleTV to make sure there is now a Folder called "Siliverlight.plugin" there. If you open the "Silverlight.plugin" Folder there should be a Folder called "Contents" and in that Folder should be two folders "MacOS" and "Resources" and a file named "info.plist".
Once I had the Silverlight plugin installed I was able to open Firefox, surf to Netflix ( I use AirMouse Pro on my Iphone 4) and start using Netflix. A couple of things that you should be aware of.
1. In order to watch movies I find it almost impossible to choose from the "Gallery View". I have to use the "Alpha Sort" view to choose what I want to watch.
2. For the first 2 - 5 minutes the screen is very laggy. After a few moinutes it starts to stream without much lag at all. Also, for me, it's too laggy to watch in full screen mode on my 50" Sony Bravia. However, windowed it works very well.
It took me awhile to figure this out and what I did use was information gleaned from the following URL.