Sorry, jobi, but you will have to hunt down the solution yourself; I have no experience with G5 desktops.
The PCI bus was changed on the G5s to either PCI-X or PCIe; there are early PCI-X models that accepts some standard PCI cards. When choosing PCI cards take care that they are dual-voltage (will work in both 3.3V and 5.0V slots).
The later ones have PCIe (often called PCI-E) and are completely incompatible. PCI & PCI-X are parallel ports and PCIe is serial.
Download a copy of MacTracker (free, and Canadian to boot) to get compatibility info for Mac models.
Dear mr.Gordeguide I have a problem and i was wondering if you would know an answer. I recently bought a G5 (DP 1800) I have old PCI cards from my 9600 mac but they won't fit.
The PCI cards have about one 11 row and one 58 row counting from the end.
The G5 PCI connector about 40*68*11 row input, counting from the end.
I read your great email remark about PCI and voltage and I was thinking what if I bend the iron front of the PCI card and put it in the PCI connector.
I could think of 3 options (with the risk of voltage damage)
I can put the 11 row PCI in the 40 G5 connector row and
the 68 PCI row in the 68 G5 connector row.
Or turn the PCI card around it would probably fit but
the PCI cards front would be backwards inside the C5.
Look for an extension cable form PCI G5 to old PCI.
The cards are old PCI Telecast Radius, miro motion DC30 and video monitor cards al 3.3v if you have any suggestions/remarks I would be very thankful.