Haiku on a Dell Dimension 9200

I've used Haiku on my little EeePC 901 for a couple of years and it works really well (although Haiku which is still in Alpha, is nowhere even close to Snow Leopard or Ubuntu Lucid in sophistication).
I did try to install it on my MacBook and on a Dell Dimension 4500 with no success at all.
I've been posting about my refurbished Dell 9200 (4GB RAM, nVidia G210) in recent days which is working extremely well. So, I tried to install Haiku using Haiku Installer from the ISO CD (latest nightly build) and this went without problems.
As before, I used Grub2's custom feature to include a Haiku stanza in the Grub menu.
It boots in just 15 seconds which is faster than any of the other four OSes I have on this machine. Nevertheless, surprisingly it's slower than the 11 seconds boot time on the EeePC 901 (1.6GHz, 1GB RAM).
Although I really haven't played with Haiku to the fullest extent, everything seems to work well with one notable exception.
One thing I very much liked about Haiku on my EeePC 901 was the ease with which I could mount every single one of the other partitions on the machine and move files back and forth as I pleased.
On the Dell 9200, I have six partitions spread over two HDDs. On the first, I have Windows Vista, Ubuntu / and Ubuntu /home. On the second I have Haiku, OSX86 and FreeBSD 8.0.
However, only one of these partitions is mountable in Haiku and that's Vista.
Nevertheless, if I look in the DriveSetUp app, all of the partitions are seen and, seemingly, correctly recognized.
So, why are they not mountable?
Beats me so I think I'll have to post to the Haiku forum about this.