In this post I will help you with your compatibilty issues, I always hear people asking "Will this work, Is it compatible". I hope this helps people.
Ram and CPU:
I do see people alot that are building who choose the wrong ram. For example, I see alot of people building a Core 2 Duo system with DDR400 ram. Well, all the new sockets e.g. LGA775, AM2 use DDR2 ram. If you use DDR ram YOUR SYSTEM WILL NOT WORK. Buy DDR2 ram for Skt LGA775 and AM2 and if possible run them in dual channel mode. Also AM2 uses DDR2 ram, DDR2 ram is basiclly the same as DDR but it just runs at higher frequencies. For example DDR400 runs at 400Mhz while DDR2 800 runs at 800Mhz, and also Ram will also have a "Pc" or "Pc2" rating. DDR2 800 has a PC2 rating of 6400 so that particular stick of ram will transfer data at 6.4Gb p/s. But if you run them in Dual Channel mode it doubles the Bandwidth so 2x 512mb sticks of DDR2 Pc2 6400 will run at 12.8Gb p/s. So if you are building a LGA775 or AM2 platform system use DDR2 ram.
Mainboards and CPU's:
Every mainboard and CPU has a FSB rating (Front Side Bus) except for the K8 processors from AMD. They do not have an FSB, they have one or more Hyper Transport Links and an integrated memory controller. The FSB limit of the motherboard is a moot point with K8 processors aside from potential BIOS limits on memory speed.
If you have a mainboard which is has a maximum of 800Mhz FSB while you have a CPU's which runs at 1066Mhz you will not get your full clock speed. E.G. you have a MB with a max of 100Mhz FSB (Yes very old board) and your CPU is rated at 133Mhz with a multiplier of 11.5 and rated at 1533Mhz you would only get 1150Mhz because the max FSB on the Mb is 100 and your CPU is 133Mhz. So whenever you are planning to buy a mainboard and cpu. Check that the FSB matches oterwise you will get a lower clock speed than rated.
Note from Nitestick:
the K8 processors from AMD do not have an FSB, they have one or more Hyper Transport Links and an integrated memory controller. the FSB limit of the motherboard is a moot point with K8 processors aside from potential BIOS limits on memory speed.
GFX cards and Mainboard slots:
If you are planning to buy a GFX card you need to make sure that you pick the right one. If your mainboard only supports AGP and you go and buy a PCI-E card then you will have alot of trouble installing your new GFX card. You must check what graphics slot you have before you buy a GFX card, you can find out by downloading this piece of software.
Once you know what Graphics Interface you have then you can to continue to purcahse your GFX card making sure you buy a card that is the same as you Grahic Interface. Also there is diffrent speeds in Graphic Interfaces. E.g. AGP,AGP2x,AGP4x,AGP8x,PCI-Ex1,PCI-Ex4,PCI-Ex16 etc.If you buy a AGP8x card and you have a AGP4x mainboard (Like me) the card will not run at its full potential. And the same with PCI-E except for PCI-E x1 because graphics card dont run on PCI-E x1 only on x4 and x16. PCI-E x1 is mainly used for sound cards, network card etc.
Mainboard Socket and CPU Socket:
The CPU socket and Mainboard socket needs to be the same E.G. Skt 775 mainboard will not work with a Skt 478 CPU, you need to have a Skt775 and Cpu for that setup to run. Once again CPU-Z can tell you what socket you have at the moment if you are planning a CPU upgrade.
Also keep in mind the FSB as I said earlier. Dont be stupid and buy a CPU with the wrong FSB and socket because you would have wasted your money.
I hope this helps you guys out there. Peace Out.