From what I could find searching, it looks like the rpm package is compressed using lzma, which redhat/cent do not support. The package is most likely intended for another distro such as SUSE or mandriva.
I would try this installer and see if it works.
http://www.real.com/realcom/R?href=http://forms.real.com/real/player/download.html?f=unix/RealPlayer11GOLD.binIf not you can try compiling it from source.