I've recently replaced my A1176's 80 GB HD into a 250 GB HD, considering the life of old driver is coming to the end. You should use Time Machine to backup everything first. Then follow the guide of HDD replacement. Good luck.
I'm now still using A1176 (T5600) as a server. I have installed 2x2GB RAM but only 3GB is usable. Mac OS 10.7.5 Lion can recognize there are 2x2GB memory modules installed but only 3GB can be used.