I had an awful time with the dreaded "Still waiting for root device" and a vanilla Snow Leopard install. The system I was attempting the install (well the 100% vanilla SL fully functional one I'm on now ) on has a single SATA hard disk and an IDE DVD drive. I attempted the install using a BOOT 123 disk and the retail install DVD and tried every possible jumper and BIOS setting to no avail. The solution that finally worked was to install a boot loader (Chameleon in my case) onto a USB flash drive (8 GB+) and then restore the install DVD onto the USB drive as well. I followed instructions from this post. I then completely unplugged the DVD drive, not sure if that's necessary or not (FYI it's the only IDE device in this machine), and booted off the USB drive with the SATA controller set to AHCPI mode and booted the install DVD.

I'm not familiar with that machine but judging be the fact that you described it as "older" you probably won't be able to use a vanilla kernel and may need some drivers installed during the initial installation that are only available in those Leopard distros. My recommendation would be to take a look at that guide and try to build a USB drive in the same fashion but with one of your Leopard distros. I'm not completely familiar with how Chameleon works so it may not work at all on your machine but it's worth a shot. If it doesn't maybe you could try some different boot loader options. Lemme know how it goes.

Jamie