Installation of the MyMedia app onto your Roku is well documented elsewhere. This article will focus on installing the MyMedia server application onto a Synology NAS. I have a DS210j, but the steps should be the same or similar for other models.
Note: This requires nominal comfort with the command line.
Here is what I did:
1) Bootstrap your device, and install the IPKG Package Management System. You can follow my previous instructions on this.
2) After installation, make sure you "ipkg update" and "ipkg upgrade" as directed in the instructions
3) Next we install Python-2.6. This will download and install all necessary files and may take a bit of time
4) Next up is the Python Imaging Library (PIL)
ipkg install py26-pil
5) Find the URL of the tarball of the MyMedia release you wish to use. Documentation is a bit sparse on the difference between releases, but in general you should use the latest one. At time of writing, the latest version was "AngyAvacado" from March 19, 2010. You want the TGZ version of the archive.
6) Pick an install folder (I use "/opt/local/opt") and fetch/expand the server tarball there
tar zxf name-of-the-file-you-downloaded.tgz
6) I created a symlink to the server folder so I wouldn't have to change any scripts that reference it later
ln -s folder-created-by-tar-command mymedia
7) Start the server, and see if you can connect to it from your Roku MyMedia channel
8) If it is not working, you can check for errors in the log
If you see this error: UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 8: ordinal not in range(128) it means you have non-ASCII characters (accents or what-not) in some of you folders and/or filenames. Unfortunately, you'll have to rename your folders/files as there seems to be a bug in the Python libraries themselves.
UPDATE: User "renojim" from the Roku Forum suggests this fix for the character issue. I'll try it soon and report back.
"One thing, try setting $LANG to en_US.UTF-8 before starting the server. The only platform I haven't been able to get accented characters in file names to work is Ubuntu 10.04 and I'm still looking into the problem."
UPDATE: If you get a error from wget complaining of bad certificates, try adding the "--no-check-certificate" option, which will ignore SSL certificate issues.
If everything is working, check my next article on how to have your server start automatically on NAS power-up.