According to everyMac.com the max ram for this machine:
M9032LL/A Power Macintosh G5 2.0 DP (PCI-X) ... is 8mb.
However, it is a 4 ram slot config. Can't determine if (4 x 2 GB) in 400MHZ DDR PC3200 sticks were ever available. Not finding online. 😟
The 2 GHz DP model with PCI-x slots (M9032LL/A) has 8 memory slots, so installing 1 GB PC3200 DIMMs in each slot provides 8 GBs of total memory. If your G5 only has 4 memory slots, it's likely the 2 GHz DP model with PCI slots (M9747LL/A). With 4 memory slots, the memory is capped at 4 GBs, because the only 2 GB DDR PC3200 DIMM that you'll find is ECC/registered memory that's typically used in PC servers, but not supported in your G5.
Check for G5 RAM at OWC (macsales.com): Search Results for G5 RAM at MacSales.com
Power Macintosh G5 RAM Max?
