I don't believe it has a pci slot, the freescale chip has a controller for such an interface, but as I've read it, its designed to be a headless network storage unit, just enough to connect it to a LAN, and run a hard drive.
If it does have a pci slot, its likely that that is used by the pci eithernet card that MDMA meantioned, as the freescale cpu I do not belive has an intergrated eithernet controller.
It is an interesting design, but it is in no way a desktop capable machine, its design as I say is as a headless network drive, an embedded system. Hackable yes, but not to the extent I think you're after.
Sorry to disapoint.
--edit--
Looking at other reviews and technical discussions, this system is a single board setup, at no point do any of the reviews I have read meantion even in passing a PCI slot, only partially setup serial (requiring some pretty nasty hacking to get going) usb2, IDE and gigabit eithernet. I'm guessing since I've not actually seen the guts of this thing that its very unlikely that this has such a slot and that the "tulip pci eithernet clone" the spec refers to is simply the controller chip, rather then a seperate card.
In short, this thing will no more run BeOS or windows then it will AmigaOS. Sorry chaps.