The PC133-based iMac G4 supports a maximum 1 x 512 Mb SODIMM and (internally) 1 x 512 MB DIMM
You cannot install a 1 Gb or a 2 Gb PC133 non-ECC module (none exist, anyway)
The internal DIMM socket is listed as "technician only". It is a fairly complex takeapart, so you may want to google for instructions first before you decide to tackle it.
Thanks
Trevor
CanadaRAM.com