Just make sure your case has ventilation.

The case is open all the time, and i have 2 more fans which i will direct them to the cpu and maybe to the video card. I just don't know how to set this voltage, and when i look at the cpu-z, the FSB is getting high. My multiplier is x12, I just rise the BUS SPEED. Is that correct? The PCIE is set to "100" and the vcore is at auto. This is at the moment.

All is right, but you will need to manually adjust the vcore. 1.3-1.325 should be adequate for operation up to 3.4GHz on an E5200, depending on the voltage regulation of your mobo.

I don't have any links with me right now, but I suggest you read up on overclocking a bit before to start pushing things.

Ok, but now I see that the FSB is actually the RAM clock (stock at 800) and my ram memory is not good and expensive. It's one of the cheapest - A-DATA. I am scared because it hits 1000MHz. Should I continue to clock or stop at 3ghz?

You need to use a lower memory multiplier/ram divider (whichever your motherboard chooses to call it) to achieve a RAM clockspeed closer to stock, while still being able to raise the FSB.

Now I use lower multiplier - 10x300 but get too much RATED FSB again - http://yfrog.com/0l21321aqjThere is flashing text - "System voltage NOT optimized" and also in BIOS I set System memory multiplier (SPD) to 2.66 and it says that the memory freq. is 800 but in windows as you can see its 1200mhz - getting too scary :)

Now I use lower multiplier - 10x300 but get too much RATED FSB again - http://yfrog.com/0l21321aqjThere is flashing text - "System voltage NOT optimized" and also in BIOS I set System memory multiplier (SPD) to 2.66 and it says that the memory freq. is 800 but in windows as you can see its 1200mhz - getting too scary :)

I'll warn you once again and then I'm done. Please read before you melt something.

Ok, first of all, I know this is not the correct forum for this(overcklocking), but we start this and I apreciate you guys helping me a lot. I wish to finish this.

I'll warn you once again and then I'm done. Please read before you melt something.

I did read some tutorials and forums. I found that for my case its good to set BUS speed to 266 or 333.1) BUS=266:I will set the cpu multiplier to x11 to get 3GHz, PCI to 100 and for the RAM I have 2 choises - 3.33x266=885MHz or 2.66x266=707MHz. At 885MHz, the ram will be clocked which i dont want couse its cheap. At 707 - will it be less productivity?2) BUS-333:The CPU would be x9 = 3GHz, PCI=100, and no idea for the RAM.Is this correct? If not, please advice.

High bus speeds are preferable, but harder to achieve stability. Try the 333 setting first and if it works, go with it. Otherwise drop back to the 266 setting. Ignore the warning about "melting" your computer, it's absurd. CPUs and motherboards have thermal protection built in which prevent this from occurring.

Ok now at 3Ghz running with no problem i made a flight this eve. The FPS are the same - in the air with many many clouds - no problem, but on the ground with buildings 20-25 fps in 2D cockpit!!! This can tell me one thing - the graphic card dies when it has to represent 3d objects in FS2004. How much CPU MHz I have to reach for 30 FPS steady? Just don't know if it the "mission" to reach 30 fps will be reachable.

2.8->3.0 isn't enough of an increase to have the impact you want. Take it up to around 3.3-3.4 and see how it runs there. As noted earlier, you may need to increase Vcore in order to maintain stability. Also, you need to watch your RAM speed to make sure it stays at 800MHz or less.