Although the Power Mac G5 (Late 2005) and Mac Pro models both use PCI-E (PCI Express) based graphics cards, the cards are not necessarily interchangeable between models.  Learn which cards work with each generation of computers.

See the article here:
Power Mac G5 (Late 2005) and Mac Pro: Graphics card compatibility between models

Similar Posts:

• Power Mac G5 (Late 2005) and Mac Pro: Graphics card compatibility between models
• MacBook Pro (15-inch, Late 2008) and later: How to set graphics performance
• Mac mini (Early 2006) and later: How to identify power adapters
• About integrated video on Intel-based Macs
• Mac mini (Early 2006) and later: How to identify power adapters