Should I check with Asus for compatibility? I've send them emails before, but no answer.
About inserting the CPU into the motherboard, for AMD CPU there is a marker that indicates how it should be placed. How is this done with Intel CPU?

The best thing to do for compatability is to look at reviews on websites for your motherboard, and look through forums as well as loooking at the specifications. Asus motherboards are well compatible, if you get no reply from them about somthing, you should be able to find out about any problems that the board has in reviews, and comments that people leave.

reviews:
1
more - google is a great place to look

Yes with Intel Chips there is a small yellow triangle on one corner of the cpu which matches with the socket. watch it done-about 2 mins in
I think that all newer chips would have this yellow triangle on them.
The E8400 is a socket 775 CPU!

Some issues:
Here are yourmotherboard specifications The E8400 will work becuase it is a core 2 duo cpu and the specs allow that.
Make sure that you buy DDR2 RAM, and a SATA hard drive. It supports crossfire, which is two or more ATI graphics cards, so don't buy two NVIDIA ones, but one is ok.

, jake

That video has good instructions. I read that the heatsink and fan of intel were very difficult to install, so I thought I try to install it first without the CPU. Is this ok? Or will the thermal compount strip stick to the CPU socket then?

It shouldn't stick to the socket, but I definitely wouldn't try it because if any does get in the socket (or scrapes off) it would be difficult to remove. If you bend a pin the cpu will not slot in correctly, and any compound lost could cause heat problems. I cannot think of a safe way that you could do that, unless you have an old Celeron socket 775 cpu or somthing then you could try it out with that. - but then you would need to re-apply new thermal interface material.

It is not that hard to slot the heatsink in place, although that video made it look easier than it is. You need to make sure that the fastener slots are pointing outwards then push down. I found it easier pushing down one corner then the other diagonal from it.

, jake

With this motherboard: p5q-e
http://www.newegg.com/Product/Product.aspx?Item=N82E16813131296&Tpk=p5q-e]Newegg.com - ASUS P5Q-E LGA 775 Intel P45 ATX Intel Motherboard - Intel Motherboards

and this RAM: CORSAIR XMS2 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500) Desktop Memory Model TWIN2X4096-8500C5C G - Retail http://www.newegg.com/Product/Product.aspx?Item=N82E16820145247]Newegg.com - Suggested Products

you need to adjust some settings in bios. I read that in order to make any changes in bios, you need to set "AI Overclock Tuner" to "Manual", even if you don't overclock any hardware. Is this correct?

except set:
- DRAM Frequency to 1066
- DRAM Voltage to 2.1V
- timing to 5-6-6-18

Do I need to adjust the northbridge voltage as well?

Yes setting the Ai Overclock Tuner to manual will probably be what you need to do. The ram by default could go to 800MHz at timings similar to those. Upping that FSB will take the ram to the speed that corsair say it can run at. Make sure that you change the voltage also if it automatically goes lower.

When you set it to those settings you said about you should run memtest86+ this runs from a bootable cd that will scan your ram for errors. Leave it running on default settings overnight (8 hours minimum) to check that it is stable at those timings. here is some information about it

With my ram errors are detected when I run it at 4-4-4-12, but at the default slightly slower speed it is ok. I already replaced it once and it still won't run at the speed stated without problems. It is my motherboard I think.

, jake

edit: I am not sure about changing the northbridge voltage/fsb voltage, it might be linked to the ram speed, in which case changing it could cause problems. Your CPU runs at 1333MHz and the ram wants to be 1066. Anyone with any experience about this please post!
Before doing the above steps and changing the settings it is best to wait for another poster.