Well, so looks like I'll have to wait for rv300 support anyway. I don't have plans to buy "another" old card!
I don't have more free space to store my "vintage" tech material.
It's the same core of the mobile radeon on powerbook g4s?
Well, I ended up seeing that. In the middle of the "Ultimate Pack" installation! 
I had to install Tiger again and I have created 3 partitions:
1) ~50gb for tiger
2) ~20gb for MorphOS
3) ~10gb for OS9
But then I found that I needed another tiny partition to boot MorphOS. Is it possible to install morphOS on the 20gb partition without destroying the tiger installation? What's used for boot manager?
When we receive Powerbook support we should get R300 3D drivers.
No one seems sure if this will be in the next revision or the one after (although I'd bet on the latter).
Your MorphOS partition may be a bit small if you want to install the "Ultimate Pack", but you probably won't use everything in the package so you could install the titles selectively.