[CentOS] kernel-devel rpm

Hello, I'm trying to install VirtualBox on a test CentOS 4.4 system following the guide on howtoforge. As a preliminary i'm trying to retrieve the kernel-devel rpm, which contains the headers and libs needed to compile kernel modules. I've tried:

yum install kernel-devel

as well as added an arch to that in this case i686 and i keep getting the msg nothing to do. The only item i can think of is i have enabled the protectbase yum plugin, if this is my problem i'd like to make this file an exception. My kernel version is 2.6.9, the default one that came with CentOS if that matters. Any suggestions welcome. Thanks. Dave.