If you want to compile the sum-module (source mirrored below), follow these steps: 
Create the Makefile in your directory with the sum-module.c
 obj-m    := sum-module.o
KDIR    := /lib/modules/$(shell uname -r)/build
PWD    := $(shell pwd)
default:
       $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules
Now do a
 make
... and the sum-module.ko is built.
 If you get something like this 
# make
make: Nothing to be done for `default'.
you need to install the kernel source and compile the kernel first (run "make" at least to the point until
 all "HOSTCC scripts/" stuff is done - this will configure your kernel and allows external module compilation). 
Make sure /lib/modules/$(shell uname -r)/build points to your build directory (most likely /usr/src/linux...).
Another reason for the above error can be, that your browser converted the TAB before $(MAKE) to spaces. 

Make sure there is a TAB before $(MAKE). 

Install it with install.sh: 
#!/bin/sh
install -m 644 sum-module.ko /lib/modules/`uname -r`/kernel/drivers/sum-module.ko
/sbin/depmod -a
(adjust the /lib/modules path according to your needs) 
 Now make a 
# modprobe sum-module 

Or if you don't want to install the module, do this: 
# insmod ./sum-module.ko
..and if your system doesn't freeze you've done it right ;-) 
 
For kernel 2.4, the Makefile would look like this: 
TARGET       := modulename
INCLUDE    := -I/lib/modules/`uname -r`/build/include
CFLAGS      := -O2 -Wall -DMODULE -D__KERNEL__ -DLINUX
CC  := gcc
${TARGET}.o: ${TARGET}.c
       $(CC) $(CFLAGS) ${INCLUDE} -c ${TARGET}.c
 (not yet tested) 
sum-module source from: http://www.win.tue.nl/~aeb/linux/lk/lk-9.html
/*
 * sum-module.c 
# modprobe sum-module.o
# ls -l /proc/arith
total 0
dr-xr-xr-x    2 root     root            0 Sep 30 12:40 .
dr-xr-xr-x   89 root     root            0 Sep 30 12:39 ..
-r--r--r--    1 root     root            0 Sep 30 12:40 sum
# cat /proc/arith/sum
0
# echo 7 > /proc/arith/sum
# echo 5 > /proc/arith/sum
# echo 13 > /proc/arith/sum
# cat /proc/arith/sum
25
# rmmod sum-module
# ls -l /proc/arith
ls: /proc/arith: No such file or directory
# 
*/
#include <linux/module.h>
#include <linux/init.h>
#include <linux/proc_fs.h>
#include <asm/uaccess.h>

static unsigned long long sum;
static int show_sum(char *buffer, char **start, off_t offset, int length) {
        int size;
        size = sprintf(buffer, "%lld\n", sum);
        *start = buffer + offset;
        size -= offset;
        return (size > length) ? length : (size > 0) ? size : 0;
}
/* Expect decimal number of at most 9 digits followed by '\n' */
static int add_to_sum(struct file *file, const char *buffer,
                      unsigned long count, void *data) 

{
        unsigned long val = 0;
        char buf[10];
        char *endp;



        if (count > sizeof(buf))
                return -EINVAL;
        if (copy_from_user(buf, buffer, count))
                return -EFAULT;
        val = simple_strtoul(buf, &endp, 10);
        if (*endp != '\n')
                return -EINVAL;


        sum += val;     /* mod 2^64 */
        return count;
}
 
static int __init sum_init(void) {
        struct proc_dir_entry *proc_arith;
        struct proc_dir_entry *proc_arith_sum;
        proc_arith = proc_mkdir("arith", 0);
        if (!proc_arith) {
                printk (KERN_ERR "cannot create /proc/arith\n");
                return -ENOMEM;
        }
        proc_arith_sum = create_proc_info_entry("arith/sum", 0, 0, show_sum);
        if (!proc_arith_sum) {
                printk (KERN_ERR "cannot create /proc/arith/sum\n");
                remove_proc_entry("arith", 0);
                return -ENOMEM;
        }
        proc_arith_sum->write_proc = add_to_sum;
        return 0;
}
 
static void __exit sum_exit(void) {
        remove_proc_entry("arith/sum", 0);
        remove_proc_entry("arith", 0);
}
module_init(sum_init);
module_exit(sum_exit);
MODULE_LICENSE("GPL");
 
 from：
http://www.captain.at/programming/kernel-2.6/