The iMac automatically should (in theory) support a FireWire disk drive. OS X may not recongnize it. I would try to insert a Mac OS X Install Disk in the DVD drive and hold option at boot, see if it shows the disk. If it does the problem is on OS X's side. Also verify that ample power is going to the drive as many FW devices have separate power supplies.
As for the iBooks. The first one without looking at it maybe a lost cause. iBooks were known for unreliablity, and motherboard replacement was oh too common of a repair that was necessary. Have you tried to zap the parameter RAM. In case you did not know, press the power button then hold Command Option P R until the boot chime is heard a second time. If that fails, try a PMU reset as outlined in this Support Document. http://support.apple.com/kb/HT1431?viewlocale=en_US&locale=en_US#faq6
If not I would seek help from an Apple technician.
As for the second iBook, I would try to boot from a copy of install media. Then proceed to check the disk under Disk Utility. To do this insert your disk while the iBook is on, then restart it and hold "c" to boot from CD/DVD. Then once Mac OS X Installer loads, click "Utilities" at the top then "Disk Utility". Select your hard drive, and click "Verify Disk". If it looks good, click out and I would do a fresh install. If not choose "Repair Disk" then repair permissions on the drive. If it still reports issues your disk is bad, and you will need to seek the help of a technician as the iBook is the last machine you want to work on inside.
Be sure to boot a installer that is either original disk, or newer to prevent issues.