how do i install a NEW system call (syscall), properly, from within a loadable kernel module ? I saw one SYSCALL_MODULE macro in OpenBSD systems.. which does the job.. but is there anything similar in linux ( 2.4.29 kernel, mandrake ).

i suggest looking into rootkits sources, that overwrite the interrups with lkms like adore.
but simple way of doing it is, adding new stuff into sys_call_table[]

ya... well. Do i run a loop through the sys_call table (maybe bottom-up) to find out an empty slot or is there any builtin function to register myself with an empty slot in the table ?