The Sad and boring System Beep Hack. It eliminates the clicking noise when you press elements such as the up/down buttons. This also makes the keyboard on an NR70 not beep (yayy!). Comes with both the palm 5 (arm processors) and pre palm 5 (motorola 68XXX family) hack versions.
Note! You need a palm 5 hack manager for a palm 5 handheld. I would recommend YAHM.
I've bundled a treo specific add a key click hack into this zip file as the key click has been removed when you use the keyboard for typing on the treo and someone asked me to make one that did just that. It cost me the price of a treo, but what are you going to do?
If you're looking for anything to do with pocketcity; I would suggest going to the official homepage: http://pocketcity.sourceforge.net/