will 1GB) PC2100 DDR 266MHZ 184pin ECC Reg SDRAM work in my imac 1ghz g4 power pc

There were (2) iMac G4 1GHz models and both support a maximum of 2 GBs of installed memory, using (2) 1 GB memory cards. The older model had a 17" screen and USB 1.1 buses, while the newer model had a 15" screen and featured USB 2.0 buses. To answer your question, PowerPC Macs do not support ECC or Registered memory. Additionally, non-ECC/unregistered PC2100 DDR-266 memory can only be used in the older 17" screen model. The newer 15" screen model uses the faster PC2700 DDR-333 memory. Both of these iMacs have (2) dissimilar memory slots. Apple designed one slot for the end-user to be easily accessible, and it takes a 200-pin SO-DIMM. The other memory slot takes a 184-pin DIMM, but the procedure to access it is a much more involved one, in terms of disassembly. End users attempting to access that memory slot when their iMacs were new, would have voided the warranty.