Are you sure you mean a system call, and not, say, a program? Creating a new system call would require creating and loading a kernel module. It would also have nothing to do with your process manager.
Now, given the open nature of Linux, this is entirely possible, but I suspect that anyone getting in to kernel hacking would know enough to a) know about /usr/src/linux-headers-* b) know how to find this info on his/her own.
So in summation, confirm that you really want to create a system call, and not a program. Then use Google, or your favorite alternative search engine.
PS - Is this a school homework assignment? If so, go earn your own damn degree.
Edit: By the list of other posts by this user, it sure looks like it.
Last edited by felixc; 03-21-2008 at 07:46 AM.