Motherboard(mobo) - This is the primary circuit board for the computer..Everything plugs into it...They come in several sizes and shapes...If you are buying a new computer this has already been pre-selected...Differnces on boards vary from amount of RAM in can hold, prosscessor size, types of connectors that can be plugged into it(USB, FireWire)..etc Unless you are building your own PC what is most important is what can be plugged in to the board such as your USB, FireWire, Comm ports..etc..Plenty of USB ports are a must...Most mouse/keyboard, digital camera's and Printers anymore plug easialy into USB ports... Central Proccessing Unit(CPU) - This is what plugs into the prossesor socket on the mobo and does the proccessing of information...The speed of these bad boys are measured in gigahertz(If your current CPU is measured in megahertz..UPGRADE)..With 1.8ghz to 2.8ghz being average speed and good enough the for the average user and 3.66ghz being damn good. But remember speed goes up so does price, and in another month or two 3.7ghz will be the new thing...(Have you seem the fiber optic proccers).....When looking at proccesors you will also notice L1 and L2 cache..to some this up "The cache is a memory locations on the proccessor that stores the most used information for easy and faster retrievel." and is measured from 8 bytes to 2megebytes...I'd say 512 bytes is average for the typical home user....The next two things on a processor are Dual Core and 32bit or 64bit architecture and how they work goes alot deeper then I can explain but here is the basics: A CPU can also be dual-core and have the basics of two CPU's in one(In a round about way)... 32 bit and 64 bit are the width and limit of data paths in the proccesor. Everyday more and more applications are going to 64bit but, it has not hit the mainstream yet...so 32bit is satisfactory unless you want to spend the cash.. RAM(Random Acces Memory) - This is the quickest and easiest way to upgrade your computer.. RAM are memory locations where information is stored but are volatile(Erased if the computer losses power)...Say your typing a letter your alomost done and the power goes out and you have not saved your work to the hard drive...The information is lost...It was stored in RAM...RAM has alot of determination on speed and how many programs you can open at once on your PC...There are several differnt types such as DIMM's, SIMMS's and DIP's.. If your looking to upgrade be sure which type is compatible with your PC...RAM sizes range from 64MB to 2GB...I would recommened at least 512mb in your PC... Hard Drive(HD) - This is your storage, where everything goes when it is saved. Hard drives range insize from less then 1 gigabyte of storage to several terrbytes of storage...And how big of one you need is up to you...If your into downloading Videos and Music the larger the better...To put it into prespective a CD holds 700mb of data(1000mb = 1gig).. A dvd hold 4.3gig of data...A high quality movie can be 4.3gigs but most can be compressed to around 640mb for a full length film w/ lower quality...So really the choice is yours...Personnally I have 2 hard drives 80gig and a 250gig...I use most of my storage for games and video editing... video eats it up pretty quick...I would recommned no less then 80gb... Graphics Card - This is what puts all the pretty pictures on your screen...The most common is the AGP(Accelerated Graphics Port) this is the port on the motherboard that the graphics card fits into...It is a specific shape like most ports...for the basic user AGP works fine.. AGP graphics cars come in several brands the most popular manufactures are ATI and Nvidia.... Make sure you have a AGP slot on you PC and you do some research..there are hundreds of sites to get performance reports on graphics cards. Some mobo's have intergrated graphics on them.... and most can not be replaced or upgraded easily(just a warning)...PCI Express is the newer technolgy of graphics cards and do not use the AGP slot on most mobo's...They use the PCI slots(used to add more ports or perihials to your PC) on the motherboard..They are faster and multipul graphics cards can be used as one...But once again more expensive and over kill for the basic user, until the price goes down. DVD/CD Drives - Floppy/Disk drives are a thing of the past due to small USB jump drives that store more information, faster...But DVD/CD drives are still needed...They range from just your basic cd player drives to you DVD/CD burners...I would recommended buying a DVD/CD burner at 48x speed. Its to easy anymore to burn your favorite tunes and movies to a DVD or CD...and if you have a digital camera this is a good way to store you pics. My Personnal PC Specs: AMD Athlon 64 3700+.................Radieon 9800 Pro Graphics Card 2x512mb Corsair Select RAM..........Asus K8V-SE Deluxe mobo 80GB Maxair SATA HD.................250GB Maxair SATA HD