Ok this is a quick and dirty method, you should use /etc/init.d/skeleton as a reference and write a proper runlevel script, but anyway here it goes:
create a file /etc/init.d/vncserver with the following content:
/bin/su user1 -c "usr/X11/bin/vncserver :1"
change user1 to whatever user you want to start the vnc server with(better not use root)
then make a symlink to runlevel 5 or whatever's your default runlevel
ln -s /etc/init.d/vncserver /etc/rc.d/rc5.d/S99vnc
that should do the trick, but as I mentioned before make a proper startup script if you can, better off that way.