We have done this on demos using mono and it will work. You must be careful to insure that you do not directly call Windows API functions directly as this would break mono compatibility, you must go through the C# classes.
However, from a practical standpoint a 1Ghz single core PC with a GUI is not very responsive.
But also take into consideration that much of the duty cycle of the PowerPMAC is constantly being used for motion control, now that PC runs more like a 500MHz PC. Furthermore, take into consideration the video adapter is fundamentally a USB 2.0 Video adapter as there were no good PCI express video chipsets at the time that would work with a PowerPC at design time.
In summary you will not get stellar performance.
In addition, consider the additional cost of the PowerPMAC Video Adapter and memory and it may cost you more than a separate PC.
We are looking into the possibility of using faster processors and video adapters in the future and at that time it may be more practical.