thats a high temp but for Pentium D`s its within acceptable levels might want to turn on the warning monitor if your BIOS has one. So if it reaches say 80C your pc will start beeping.
The plastic things on your mobo are ok, normally you have brass mounts but some motherboards do come with plastic ones too. So that`ll be fine the good thing about those ones is if one is out of place it at least wont short your motherboard
Hard drive noises are hard to pin point mine always make a racket but have not failed yet, Although iv heard many with little clicking noises which have failed so its hard to diagnose without using the software.