Kernel module problem

Dear All,

i’m installed centos 5.0 following the criteria mention blow this link

then installing zaptel

error produce
grep: /lib/modules/2.6.18-8.1.15.el5xen/build/include/linux/autoconf.h: No such file or directory

You do not appear to have the sources for the 2.6.18-8.1.15.el5xen kernel installed (under /lib/modules/2.6.18-8.1.15.el5xen/build).
make: *** [modules] Error 1

how can we solve this problem, plz tel me

Thanks in advance

Yum install kernel-devel