How to bootstrap NetBSD/sparc64?
The simplest method is to grab an INSTALL kernel packaged with a miniroot with built-in sysinst and boot from that. You can netboot it, place it in a Solaris root partition and have the solaris bootloader load it, or use a properly built ISO image burnt onto a CDROM. But if you need to share a disk with Solaris you may need to resort old method of installing from Solaris.