To get something to run on startup the easiest way is just to add the command to /etc/rc.local but if it is a complex proccess then you may want to create a seperate startup script.
To keep a proccess alive there are a few ways.
1) A script like "while [ 1 ];do somecommand;done"
2) You could add a line to /etc/inittab
3) The best and most stable solution would be to use daemontools:
http://cr.yp.to/daemontools.html
