I want to buy iPOD. 
I want to down load music with extension *.ra which is played by real
player. Can this be downloaded on iPOD? If cannot then can I convert
*.ra into MP3 format?
How can I convert *.ra into *.mp3 format?

Greetings!
Unfortunately the .ra format is not playable on the iPod at this time.
 Currently the iPod can only play songs with the extensions, AAC, MP3,
VBR, AIFF and Wav.  The good news is that converting from RA to MP3 is
relatively easy.

To do this there are a number of simple shareware programs available
that you can download.  The best of these seems to be Akram Audio
Converter.

"Akram Audio Converter lets you convert among audio files. Convert
RAM, RMVB, RA, RM, and RMJ files to WAV, MP3, OGG, or WMA files.
Convert WAV, MP3, OGG, and WMA files to Real Audio files (RM). Convert
WAV, MP3, MP2, MP1, MPEG, MP4, AAC, OGG, AVI, MPC, MOV, QT, or 3GP
files to WAV, MP3, MP2, ACM, AC3, MP4, AAC, VOX, or AMR files. The
program also supports extracting audio from RealVideo files and
ripping audio CD tracks to WAV, MP3, WMA, and OGG files."

http://www.download.com/Akram-Audio-Converter/3000-2140_4-10392085.html?tag=lst-0-3

If you have any questions, please request a clarification before
rating my answer and I will be happy to help.

Best,
djbaker-ga