It's because you are using a 32 bit OS
We are using the OS:
uname -a
Linux localhost.localdomain 2.6.9-78.ELsmp #1 SMP Wed Jul 9 15:39:47 EDT 2008 i686 i686 i386 GNU/Linux
But trying to run a 64 bit installer
postgresql-8.3.8-1-linux-x64.bin
(Notice the 'linux-x64').
Download the 32 bit version of the installer and you should be fine.