OK. Thanks to the command-line ideas from Jeroen and Cedar, I was able to get much further (plus I know how to get into the command-line now! Yay!), but I'm not exactly sure what caused it to finally see the USB stick for the Installation media step.
The installation seemed to go OK and finish OK, but on restart, the iMac will not boot. I get the Mac icon that means bootable media cannot be found.
I'm guessing maybe I made a partitioning mistake or a partitioning quirk or grub?
Here is my partitioning setup:
LVM VG vg1, LV lv1 - 398.5 MB Linux device-mapper (linear)
#1 398.5 MB f ext2 /boot
LVM VG vg1, LV lv2 - 398.5 MB Linux device-mapper (linear)
#1 398.5 MB f HFS /boot/grub
LVM VG vg1, LV lv3 - 75.2 GB Linux device-mapper (linear)
#1 75.2 GB f ext4 /
LVM VG vg1, LV lv4 - 4.0 GB Linux device-mapper (linear)
#1 4.0 GB f swap swap
SCSI2 (0,0,0) (sda) - 80.0 GB ATA WDC WD800J-40GB
#1 32.3 kB Apple <---------------------------------------- bet this is the problem? I should have deleted this first?
#2 80.0 GB K lvm untitled
25.1 kB FREE SPACE
SCSI6 (0,0,0) (sdb) - 4.0 GB General UDisk <-------- my thumb drive
If the USB doesn't work this time, I need to dig through a filled-up cave for blank CD-R, DVD-R, or DVD+R discs (Thanks, Ken!). Hopefully, the CD/(DVD?) drive will work.
The Built-in Ethernet hardware is apparently bad, and MacOSX still would not recognize either, but the Debian Installation did recognize the Apple USB-to-Ethernet dongle.
Anyway, please offer any advice on where I may have messed up, so I can get this thing booting.
BTW, any recommendations for a lightweight GUI to install? I need this machine mostly for gcc (some g++) and TCP/IP and thread programming, gdb, SSH/SCP.
Thank you!