I have Three Small drives (6G, 3G, 10G) on my G3 tower, I have set up a concatenated RAID of the three drives and it works I start too install tiger (CD not the DVD) and it restarts for the next disc and the starts to boot and it turns to the gray /. I knoe the Hard Drives and the disc is fine I think it may be a hardware issue.
Are you sure you're booting from the right hard drive? These setting can be changed within the firmware setting, I think. To get to the firmware settings, you hold down a certain key. Google "Mac OS X firmware" or something like that.
I do not think Mac G3 Has raid support. I have looked at my mac g3 motherboard and I see nothing but the ata100 thinks I can't think of there name right now.
I think the only way you can really do raid is with serial 150 interfaces. I have never seen them done with ata100 interfaces. Either way this info isn't going to help but raids are very hard to set up.
Raids also need special software installed when the os is being installed. This requires what ever raid hardware your useing to have the drivers installed as you installing mac os x. I don't know how to do it with mac you should try support. I have seen my dad do it on his windows xp computer where you push f6 before installing and it will promt you asking for a driver. This becomes an issue because if the company you got your raid from is apple support you will never get the driver for mac os x to reconize it.
What I recommend is get one really big hard drive or install mac os x on the small hard drive 3gb and put all your apps on the other hard drives it won't be raid but it will give you the same basic principle.
Another thing you should look at is that if you are using more then 3 hard drivers on one interface it will not work each of those plugs on the motherboard only support 2 devices.