The problem booting the hard drive-installed Solaris from DVD, in my previous post, was just a typo (boot_archive, not boot-archive)
I decided to repartition the extended partition and get rid of the extra 2 GB. I created a FAT32 partition at the normal maximum, 32 GB, for file storage. I reinstalled Ubuntu, giving it 20 GB. Then, I used the Solaris DVD to boot into the hard drive image, edited the menu.lst, and used installgrub to update.
Next project: enable the via-rhine chipset Ethernet, onboard the VT8237 Southbridge on this P4VMA-M chipset motherboard.