This section is about the more advanced components of a computer.

Video Card: This processes the graphics for the computer. The better the card the better the graphics look especially for pictures, video and games.
I would recommend getting a direct X 10 capable video card like the NVidia® 8400 series or an ATI® Radeon® 2400 series for any low end PC to enhance movies and graphics on programs in general, an NVidia® 8800 series or ATI Radeon® 3400 series for a middle end machine to improve visuals for gaming, movies and programs. Nvidia® 260 series or ATI® Radeon® 4350 series for a high end gaming PC drastically improves games visuals, High Definition movies and enhances program visuals a little.

Audio Card: The Audio card processes the sounds for the computer. The better the card is the better the sound will be especially for games and high definition movies and videos. Any upgrade here will make your music and videos sound better but if you are aiming for a surround sound experience I would recommend a Creative X-fi card, any of these X-fi cards allow for 5.1 to 7.1 Dolby Digital Surround sound and even if you are using  stereo you should notice a difference from your built in audio.

Motherboard:The motherboard holds and controls all of the components inside the computer (CPU, RAM, etc). This is important because you have to buy all of the components according to the specifications set by the motherboard. I would recommend  a motherboard a that has an Intel Socket 775 for a low or middle end computer. I also recommend a motherboard with an Intel Socket 1366 for higher end computers. I would also recommend a motherboard with a PCI express x16 slot for a good video card such as those discussed above and has support for 4-8 GBs of DDR 2 RAM for low and middle end computers. (DDR 2 is Double Data Rate times 2 (Which is fast and is capable of higher capacities than DDR)). I recommend a motherboard that supports DDR 3 for gaming and other RAM intensive Programs.