Should i use the thermal pad? or use the arctic silver 5 (i bought the silver 5 already)
If you do not want to overclock, use the stock Intel HSF that comes w/ your CPU. Do not use the AC5 because the Intel HSF comes pre-applied w/ thermal paste.
And for the heatsink and fan I'll just use the one that comes with the intel core 2 duo for now.
At the stock clock, that will be fine.
The antec 900 case will help cool the cpu down won't it?
Not really. Maybe a little.
How do i overclock? and what are the risks?
Search the forum, and research the internet on that subject. Monkeys can OC a CPU. It has nothing to do w/ skill and it is not difficult. The risks are minimal. Do your research.