Most of the conversions can be handled by ffmpeg which comes with a amazing number of codecs.
To convert your file, try the following command:
ffmpeg -i file.rma file.avi
Useful information about a file can be retrieved using the file command. Remember that avi or rma are just containers, so two avi files may not use the same encoding for audio or video. That's why a conversion from ram to avi may not work in all cases, if one of the codec used in the original file is not supported by ffmpeg.
For example, on my computer, with three different files:
> file file1.avi
file1.avi: RIFF (little-endian) data, AVI, 720 x 400, 25.00 fps, video: DivX 4, audio: MPEG-1 Layer 3 (stereo, 48000 Hz)
> file file2.avi
file2.avi: RIFF (little-endian) data, AVI, 608 x 336, ~24 fps, video: Motion JPEG
> file file3.avi
file3.avi: RIFF (little-endian) data, AVI, 640 x 304, 25.00 fps, video: DivX 4, audio: MPEG-1 Layer 3 (stereo, 24000 Hz)