[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.