Looking at mac tracker, your system is designed for PC3200 DDR SDRAM, but not ECC. It will probably not work.
The manual Denz posted in the listing does explain it...
http://manuals.info.apple.com/en/imacG5_17inch_memory_.pdf
On page 2, copied and pasted here:
1. iMac G5 computers work with memory modules (DIMMs) that meet all of these
criteria: PC3200, 2.5V, unbuffered, 8-byte, nonparity, 184-pin, 400Mhz DDR SDRAM.
2. There are two RAM slots. The maximum amount of RAM you can install is 2 GB. You
can use RAM module sizes of 256 MB, 512 MB and 1 GB, in either slot.
3. DIMMs with any of the following features are not supported in the iMac G5 computer:
registers or buffers, PLLs, ECC, parity, or EDO RAM.
Plus, if you bought the ram, and for some reason it did work - if you all of a sudden started having problems with your machine, it would most likely be traced back to using non-supported ram.
