xktock.c is a program that renames the xk*.* files to ck*.* in the current directory, so that you can compile them with the Makefile, and so that the include files will have the right names. Compile xktock with your C compiler (e.g. "cc -o xktock xktock.c") and then run it (e.g. "xktock xk*"). Before doing this, you should have put all the xk* files in their own directory and cd'd to it.