smida7, welcome to Apple Discussions.
Since you mentioned PC100 RAM, you probably have an older Mac. Look at these G4 specs & tell us which one you have.
http://www.everymac.com/systems/apple/powermac_g4/index-powermac-g4.html The older Macs came with PC100 (100MHz) RAM, but you can install PC133 RAM because it's backward compatible. That is, PC133 RAM will operate at PC100 speed. Your Mac can probably use up to 2GB of RAM (4 each 512MB modules) while booted in OS X, however, only 1.5GB may be recognized while booting MacOS 9.
On your hard drive question, look at these links.
What Macs natively support large IDE drives? (over 128GB formatted)
http://forums.xlr8yourmac.com/action.lasso?-database=faq.fp3& layout=FaqList&-response=answer.faq.lasso&-recordID=34188&-search
How Big a Hard Drive Can I Put in My iMac, eMac, or Power Mac?
http://lowendmac.com/macdan/05/1024.html
Using 128 GB or Larger ATA Hard Drives
http://support.apple.com/kb/HT2544
The Power Mac Storage FAQ
http://forums.macnn.com/65/power-mac-and-mac-pro/246391/the-power-mac-storage-fa q/
Possible Alternative - SpeedTools ATA Hi-Cap Support Driver: Allows the use of extended capacity ATA drives (drives greater than 128 Gigabytes in size) on older (Pre Mirrored Door) G4 and G3 Macintoshes running MacOS X versions 10.2 and later. Cost $24.95
http://www.speedtools2.com/ATA6.html
Possible Alternative 2 - Larger than 128GB drives can be used by adding a PCI ATA/100 or ATA/133 controller card, one which is 48-bit LBA compliant; or by adding a PCI SATA controller card and using SATA drives.
If you install an external firewire HD, you are not limited in size.
Cheers, Tom 😉
