From Mactracker:
PowerMac G4 Mirrored Drive Door, released August 2002:
M8787LL/A = Dual 867MHz (133MHz FSB)
M8689LL/A = Dual 1.0GHz (167MHz FSB)
M8573LL/A = Dual 1.25GHz (167MHz FSB)
PowerMac G4 Mirrored Drive Door FireWire 800, released January 2003
M8839LL/A = Single 1.0GHz (133MHz FSB)
M8840LL/A = Dual 1.25GHz (167MHz FSB)
M8841LL/A = Dual 1.42GHz (167MHz FSB)
So there you have it, there was a dual-1.0GHz PowerMac G4 in the initial MDD version release. Quote from Mactracker:
"dual 1.0GHz and 1.25GHz models shipped with 256MB and 512MB RAM, 80GB and 120GB hard drives, a DVD-R/CD-RW SuperDrive, and an ATI Radeon 9000 Pro graphics card for $2499 and $3299 US, respectively."