My kernel version: Linux rh53dell 2.6.18-128.el5 #1 SMP Wed Dec 17 11:41:38 EST 2008 x86_64 x86_64 x86_64 GNU/Linux

To have a Linux kernel module development environment on RedHat53, your should install many rpm packages.
In other words, you must have gcc, kernel-header and kernel-devel packages, etc installed on your system.
Now I’d like to show your all of the required rpm packages name:
 
libgomp-4.3.2-7.el5.x86_64.rpm
kernel-headers-2.6.18-128.el5.x86_64.rpm
glibc-headers-2.5-34.x86_64.rpm
glibc-devel-2.5-34.x86_64.rpm
gcc-4.1.2-44.el5.x86_64.rpm
libstdc++-devel-4.1.2-44.el5.x86_64.rpm
gcc-c++-4.1.2-44.el5.x86_64.rpm
kernel-devel-2.6.18-128.el5.x86_64.rpm
After install above rpm packages one by one, you can compile your kernel module.
Good Luck :)