In order to simulate circuits, the simulator engine must be compiled. The GNU C++ compiler, version 2.7.2, should be able to successfully compile the engine. Unfortunately, there are known template instantiation problems associated with version 2.6.3 of the same compiler.
To compile the simulator engine, simply change to the cktsim directory and type make. If there were no errors during the compiling and linking, a digisim executable should be created in the directory. This binary will be executed as a subprocess by DigiTcl -- there is no need to run the executable directly.