Well buddy,u have a prescott cpu out there.
So those temps are normal for that proccy,nothing astonishing abt it.
At idle it will be around 55 and go on arnd 70 on full load.
Things to do to keep it cool:-
1]Keep ur cabinet fully ventilated,so add intake and outake fans.
2]Also clean the heatsink,this is the thing which most of the people forget.
Building up a cabinet and keeping it like that doesnt mean that ur work is over.You shud be cleaning the dust inside once a month or so.
3]Properly arrange the wires inside,so they wont obstruct the air flow.
4]Get a good cpu cooler if u can afford it.(around 2000/-).This alone will be responsible for huge drops in temps.My p4 2.8 went from 70 to 52 on full load
when i installed star ice cooler.
5]Reapply thermal paste once every 6 months.