Hi Everyone, and a warm welcome to the forums! 🙂
It's not the QT Update causing it, and it's not old PPC Hardware causing the problems.
I finally got the QT7.6 update, (Dial-up takes awhile), I installed it and Civ 4 runs as good as always on my old G4.
My advice to every one is to first get the Download for real here...
http://www.apple.com/downloads/
Then Safe Boot from the HD, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, it will try to repair your Disk Directory while the sippnig radian is happening, so let it go... if it takes way to long, then you must find another way to repair your HDD first, like DiskWarrior).
Then Re-apply the Update & reboot.