Yes, they actually were complete PCs on a PCI card, they only shared storage and the monitor (but not the graphics chip, that was separate: they used special Y cables that connected the Mac's graphics to the card to the monitor, so only one platform had control over the monitor at any given time).
But even back then, you could buy an entire PC system, including a decent monitor, for the same or less money than an Orange Micro card, so unless you desperately needed to save space, they weren't economically feasible.
tooki