You will need to boot into something like a live CD or perhaps terminal mode on your Linux install disk.
To get a terminal from the install disk, type ctrl-alt-F1 as soon as the disk has booted.
Once in terminal, cd to /mnt and create a directory (mount point) for the Linux install and mount the partition to this mount point. Now you will be able to go into xxx/etc/rc.d and change any files. Make sure you cd to xxx/etc from the mount point. ie do not just type cd /etc.