How do I play a real media '.rm' file

You may be in the need to install Restricted Extras on your system. You can do it by dropping sudo apt-get install ubuntu-restricted-extras in a terminal

Additionally, information provided in this page can be useful, specially this which refers to Real Media, posted here for your convenience.

Introduction

RealPlayer is a media player originally developed by RealNetworks in 1995. It supports a number of audio and video codecs such as realaudio, realvideo, mp3, ogg vorbis and theora, h263, and AAC. RealPlayer for Linux is based on the open-source Helix Player which can be found at the Helix Community Website.

Please Note: RealPlayer is proprietary software, is not supported by the Ubuntu community, and is not available from the official Ubuntu repositories. It is located in the non-free section of third-party repositories which the user must specifically enable.

Which lead us to the possibility of the installation (alternatively, of course), of the Real Media Player for Linux, which seems to be discontinued but you can find older versions in the "Helix and RealPlayer Archive"

However, the installation of the sole codec should do the trick. I suggest you to try the restricted extras in first instance and to try again the .rm playback using your favorite media player.

Good luck!

MPlayer plays most MPEG, VOB, AVI, Ogg/OGM, VIVO, ASF/WMA/WMV, QT/MOV/MP4, FLI, RM, NuppelVideo, yuv4mpeg, FILM, RoQ, PVA files, supported by many native, XAnim, RealPlayer, and Win32 DLL codecs. It can also play VideoCD, SVCD, DVD, 3ivx, RealMedia, and DivX movies.

SMPlayer (GUI for MPlayer)