Curious which verison of the CentOS you are running?

try typing uname -a in the command line

if you see

Linux XXXXXX 2.6.18-238.19.1.el5 #1 SMP Fri Jul 15 07:31:24 EDT 2011 x86_64 x86_64 x86_64 GNU/Linux

Then you are running 64 bit of CentOS.

Command cat /etc/redhat-release  will show you the version of theCentOS