Windows 7: Should I try to overclock with my spec?

You can start with this thread: HOWTO: Overclock C2Q (Quads) and C2D (Duals)



When you're done, just google your parts and continue reading. You're going to want after market cooling, so I'm sure you'll find your way to a few reviews along the way.

Go for 3.6 400*9 on stock voltage. That is the best oc for 8400. Do it from bios and set voltage for cpu on 1.225. Turn of Eist and that second option (cant remember, need to see what is it called when i get home).
Turn of any "turbo" and stuuf option you have and put pci-e frec. to 100. Thats about it, 8400 was made for 3.6!

Why would you do any of that? That's not very good advice.

By entering voltage and shutting off Speedstep you're losing really neat power saving features that do not interfere with a stock vcore OC, so it's counter productive. At only 3.6GHz, you really don't need to touch a thing.

Doesn't eist , cia and those stuff make oc'ed machine unstable?, and doesn't auto voltage raise your cpu vcore vhen you raise fsb? - this is not good expecially if you have a stock cooler.
Yes I agree with you about power saving but it is not so hugh difference like on air conditioner or fridge...

Turning those features off can provide stability, but that's in cases of really high overclocks. If your systems isn't stable with small overclocks, then something isn't right.

With something as mild (for the E8400) as a 600MHz bump, as you pointed out, the core will handle it with ease. Yes, if you leave it on auto voltage will be adjusted, up and down, but not more than the chip's specs list as safe, which is between 0.85 and 1.3625 volts.

If you only have stock cooling, you shouldn't be overclocking anyway. Yes, lol, keeping Speedstep on isn't going to save you as much money as never turning on your air conditioner , but, over time, the money is going to start to add up.

You've been given very good advise. Overclocking is something that takes a lot of research, trial and error and time. Cooling is your friend and increasing the needed voltages in very small increments. Research your CPU, memory and North bridge It's a long time consuming process and can get to be like an addiction.
If not done properly not only can you brick your system but you reduce the lifespan of your CPU heat is your enemy also you'll have to remember when researching that what others have achieved with the same parts not every system even with the exact same parts will overclock the same. Your bios is your friend don't use software as has already been suggested.
Ask yourself what it is your trying to achieve and why and take your time.
You'll need a temp monitoring program,cpuid,prime95 for stress testing and stability. You'll find out all this going to sites dedicated to overclocking. Good luck enjoy. Fabe.