I wouldn't try using a SmartStart 8.70, since 8.50 is what they call for on the HP site. Also, be sure you have a good download (check MD5) and a good CD burn. Try a different CD-ROM drive. On the newer servers, I have seen this happen with the Service Pack for ProLiant DVDs. Converting them to bootable flash drives fixes that. I would not try that on a G4 though, since I don't think it has USB 2.0 support.