In your ISE installation, take a look at the following file: $XILINX/doc/usenglish/books/docs/dev/dev.pdf
It has a chapter called "Design Flow" which contains what you ask for. If you want even more details, take a look at the individual chapters in that document for the tools you are interesting in (e.g. ngdbuild, map, and par). Also, $XILINX/doc/usenglish/books/docs/xst/xst.pdf contains information about the Xilinx synthesizer.
/Andreas