So, you're thinking about building your own PC! Fist off let me start by saying congratulations, you're coming into a world of headaches and torture like you've never experienced before.

Now that that's out of the way, lets get started.

When deciding to build a PC, I usually draw out a vague description of what I want in my PC, and what I want to do with it. Are you going to have a lot of I/O cards and what slots they use (PCI slots, AGP Slots) you want; What kind of controllers do you want (SATA, IDE, SCSI, other); dial-up or high-speed internet (any what type); do you need a network c; do you have peripheral devices and what kind of ports are they going to use (USB, USB 2.0, fire wire, Ethernet, parallel & serial ports); is speed important (I'm playing a lot of games, just using it for internet, Business PC); what Operating System will I be loading (Windows, Mac, Linux); Is style important?

Our Example:

I/O cards?	Total: 1 AGP & 2 PCI slots (minimum) AGP video Card PCI modem PCI Ethernet adapter
Controllers?	Total: 2 IDE controllers (minimum) IDE (1 Hard drive 3.5" internal) IDE (1 CD burner 5.25" external) Technically you only need 1 IDE controller because it will support 2 devices, but I prefer separating them both.
Hard Drives?	10GB I would NOT recommend getting a hard drive with less than 80GB even if you don't think you'll use the space. I'm using this 10GB because it just lying around.
Peripheral Devices?	Total: 2 USB port (USB 2.0 preferred but not required) Total: 1 Ethernet port 1 USB printer 1 USB Mouse 1 Ethernet port for network access
Is speed important?	Not today
What OS will I be loading?	Windows
Dial-up or high-speed internet?	dial-up
Style?	moderate importance.

I know this maybe a bit overwhelming, but as you get more familiar with what you want, you'll know what you need. This will save a lot of time in the end.

After figuring out what I need/want, I usually shop for the motherboard first, or a bundle with motherboard and processor (CPU). In our example I will be using a DFI lanparty board that I purchased through TigerDirect.com because it's part of my lying around collection.

This DFI board is a standard ATX form factor. So finding a case will not be difficult. We need to find a case that can support (or have space for) the items above and the ATX form factor. Take a look at this link for cases. As with most case descriptions, they list the number of 5.25" bays and 3.5" bays (and whether there internal or external). From before, we only need 1 internal 3.5" bay and 1 external 5.25" bay.

Next step read the manual (that came with the motherboard) to find out what kind of processor and memory (RAM) it will support. I can see that my DFI board will support 32 bit processors from AMD and speeds from there Duron line to 3000+. For Memory, it supports PC2100, PC3200, and PC4000 DDRRAM.

To begin assembly here's what you'll need:

Case
Motherboard
Processor (CPU) and heat sink
Thermal Grease
Memory (RAM)
Screwdrivers
Anti static wristband (optional, but highly recommended.)

Installing the Mother Board:

As you can see the case is totally empty. First off, I'm going to install the screws into the case. You need to be sure to line the screws up with the holes that are in the motherboard.

There is a plate or piece of metal that came with your motherboard. This lines up the port on the board with the back of the case, and usually just pops in.

Place the Wristband on your wrist and ground it to a METAL part of the case.

Sometimes you get Plastic spacers with your motherboard you should install these now and then gently place the motherboard into the case.

Screw in the motherboard.

Installing the Processor:

Now that the motherboard is installed, you can install the processor. Be sure that you are still using the anti static wristband and take the processor out of the package. Line the pins of the processor up with the pin holes on the socket. The easies way is to note that one corner of the processor is notched or cut. This corner points towards the raised part of the socket.

Make sure the arm or lever of the socket is in the up position.

Set the processor down. It should almost fall into place. NO FORCE is necessary.

Once the processor is seated lower the lever into the closed position.

Installing the heat sink:

Once the processor is installed it's time to put in the heat sink. You'll need to place a thin layer of thermal grease on top of the dye. Set the heat sink on top of the processor being sure to line up the ledges. Try not to slide it around to much.

DO NOT USE THIS PICTURE AS AN EXAMPLE OF HOW MUCH THERMAL GREASE TO USE. This Processor is old and I was showing someone how too add the thermal grease and they got a bit carried away. A small dab of thermal grease directly on the Dye should be sufficient.

Clamp one side down and then the other. You can you use a screwdriver for this but I would not do it unless you have to.

Once clamp you should be able to see a three pronged fan power connector on the motherboard. Read the motherboard manual to find out if there is a particular one for the CPU fan. Plug in the heat sink.