[CentOS] x86_64 package mess ?

Hi,

I just installed CentOS 5.4 on a 64bit-server. It's the first time I 
work with this sort of hardware. Doing rpm -qa | sort | less shows that 
most of the packages seem to be installed twice: once for i386 
architecture, and then again for x86_64.

Is this normal? Or did I mess up something during install (thought I 
wouldn't know what)?

Niki