The two different types of RAM specifications in two locations make upgrade
a chore if both are replaced to gain the maximum possible capacity increase.
Both memory chip types are listed here, for all models the USB2.0 iMac G4:
http://eshop.macsales.com/shop/apple/memory/iMac/G4_1.0GHz_1.25GHz
Battery 1/2AA 3.6V Lithium:
http://eshop.macsales.com/item/NewerTech/BAA36VPRAM/
The easiest upgrade is user-accessible slot under the metal tin inside the bottom
of the iMac G4, next to the AirPort Extreme Card slot location. The other involves
a take-apart and detailed instruction along with supplies (thermal paste, torque
to spec of screws, wires that are easily broken that are in the way) which should
include a replacement 1/2AA 3.6V Lithium battery that is in the vicinity of harder
to reach Standard 184-pin RAM chip further up inside on the logic board.
• Mr Tote's iMac G4 1.25 USB2.0 Take Apart:
http://www.mrtotes.co.uk/page1/page1.html
• iMac G4 Take-apart for Drive, RAM, Battery, etc:
http://www.xlr8yourmac.com/systems/imac_g4/imacg4_takeapart.html
Since the supported total of memory capacity involves replacement of 184-pin chip
located on the logic board, and a laptop size 200 pin chip, that in a USB2.0 iMac 1.25
is the same memory upgrade chip used to upgrade the Mid - 2005 iBook G4 12"/14".
The total of 2GB should help the computer run the last supported OS X 10.5.8. Also
note the OWC macsales offers an SSD Mercury Legacy for use with ATA/PATA.
Hopefully the iMac G4 can find useful purpose, be on the look-out for replacement parts
source, and the official Apple service manual in PDF is helpful in process of maintenance.
Good luck & happy computing!