I have just removed the DVD drive from my G5. I am keen to try out setting up a RAID on the existing 2 160GB internal drives I have in the Mac. It is possible/viable to put a 7200 RPM Maxtor IDE drive in the spot where the DVD drive was, to boot from this, and then to se up the 2 160 GB internal SATA drives in a RAID set up using Soft Raid? I would have thought so, but has anyone done it? How would I change the bios so that it boots from the new IDE drive?

It may work. There are no BIOS settings in Macs...you simply select which drive to boot from in the System Preferences > Startup Disk. As long as the Mac "sees" the drive and you can get OS X installed, it shouldn't be a problem.

The software RAID works well...I have set that up on mine before.

C

The system checks through the data chain for bootable drives, the CD bay is one of the chains checked, so yes that would work. I missed that you were using the older connection. If you have a system on it, it should work fine and is a good thought for your need(s).