Just to report ... but it has only registered 512mb ram so i guess i have not connected it properly, should i just push it really hard?
In my experience you do have to force the RAM a bit. Because of the position of the slots (the innermost slot is the tricky one, as you can't get your fingers to the side catches easily). However, many messages back in this thread there was a stark warning from someone who had damaged his G5 by forcing the chip(s) in too strongly, dislodging the drive immediately above.
Coincidentally, one of the chips I bought from Crucial turned out to be faulty (they replaced it promptly). The only way I could tell this was because applications kept quitting unexpectedly (the memory registered and appeared to be OK). Eventually I ran the full test on the hardware checking disc that came with the G5, which identified the error (this takes some time). I confirmed the result swapping the suspect chip into the other slot, just to check it was the RAM and not the slot that was at fault.