• Basic Home PC (a.k.a. Budget PCs): Inexpensive, basic computing, parts usually of lesser quality, hence the low price.
• Desktop: Good for most home and business applications, there are usually several lines to choose from.
• Slim line: Smaller, thinner units designed to save space. Because they are smaller they may somewhat less upgradeable than desktops or workstations.
• Internet appliance: Inexpensive, used for Internet, email, light processing.
• High end video gamer PC: Pricey, fast CPUs, more ram, big hard drives, high end video chips or cards for video gaming or other high end applications.
• Business class PC: Usually more expensive than "Home" class PCs. Said to be made of higher quality parts and have less obsolescence with parts over annual model lines and subsequent model lines.
• High end Business class Workstation: Powerful CPUs, lots of ram, high end video, big hard drives for workhorse applications like CAD/CAM, engineering and analytical modeling applications, audio & video production etc.
• Laptop: 1). Entry level laptop, basic computing.  2). Mid-line laptop, basic and advanced processing tasks. 3). Heavy duty laptop, high end computational applications like audio and video production, engineering applications or gaming. Need a laptop?
• Tablet PC: Works like a pen & paper - but on a computer. Cool! Check them out here:  http://www.microsoft.com/windowsxp/tabletpc/evaluation/about.mspx
• Build it yourself PC?!: Sure, why not? It could be a challenging and fun project in which you could hand pick all of your components like: PC case, Motherboard, CPU, RAM, hard drives, RAID cards, video cards, power supply, DVD/CD ROMS, operating system etc. Truthfully, you should have a little knowledge of computers or be a tinkerer, a putzer, a hobbyist and be somewhat mechanically inclined (AND patient) to build your own computer - but it can be done. Many "do-it-yourselfers" are very satisfied with owning an operating a self built system because they can be easier to support and made from non proprietary parts. It beats having to deal with the big, uncaring, proprietary PC manufacturers (Like having to send your laptop to GATEWAY TO HAVE THEM FIX IT! ). 

Dizzying...isn't it?  Well, it only gets worse. Yes it's complicated, even for technical people. There are about as many different choices of computers and hardware configurations as there are for automobiles: small, midsize, large, vans, SUVs, crossovers, gas, diesel, hybrids (don't buy the Yugo!).

1. PC performance is usually related to price. PCs are similar to sports cars. If you want to go 0 - 60 in 3 seconds, you'll need to shell out some $$$. The cheaper a unit is priced, the less powerful and slower it usually is.
2. Get a PC that fits your needs. If all you need is a basic system for Internet and email, don't buy a high end 64 bit gamer system for $3000.00.
3. Preloaded software. What software comes standard? What is extra? Is DVD/CD media included for a Windows reload if needed?
4. Relliability. This is the difficult one. It can be hard to find accurate, unbiased data that reports the reliability of computers. The data also changes from year to year (it's a shell game folks). All computers breakdown and have problems. Making it even more sketchy is that with any manufacturer some system models in a product line may perform better or worse than system models in a different product line. An example for me is Gateway. They've made decent desktops for years, but have had quality and reliability issues with some of their laptops (I know first hand because of my $1200.00 paperweight! Ohh that one still hurts).
5. Warranty. Is a 1 year or 3 year warranty included? Is an extended warranty something that you may want? READ THE FINE PRINT!
6. Hard Drive Warranty. Note or ask about the hard drive warranty or possibly an extended warranty on a hard drive (hard drive is the physical disk inside your computer, not your computer itself). Unfortunately with an OEM system (Original Equipment Manufacturer) the hard drive warranty is less than if you bought the hard drive separately. A hard drive bundled with an OEM PC may only have 1 - 2 years of coverage under a general warranty on the computer whereas a hard drive purchased separately can have a 3 - 5 year warranty supplied by the hard drive manufacturer.
7. Watch for REBATES. You can get great deals with $100, $150, $200+ manufacturer rebates.
8. Looking at a used or refurbished system?  There are a lot of unscrupulous people (as well as scumbags) selling used computers folks:
9. Get a warranty. A 30-90 day warranty may give you a warm fuzzy feeling, but may not offer a lot of protection. Often this is what you'll get on a used system, if you get any warranty at all. But, some refurbished/used systems can offer good deals.
10. Know the return policy (I've seen 7 day return policies on Ebay, red flag).
11. Check to see if the original CD/DVD Windows Media comes with it in case you need to reload the operating system.
12. Look for recalled products before you buy. www.recalls.gov
13. Do not RUSH into buying a PC. Do your homework! You already know that, but we all do stupid things (I bought a refurbished Gateway laptop...did I tell you that I hate Gateway? Oh, I digress). Since there are many different models to choose from, many different product lines, with many different hardware configurations, t-a-k-e  y-o-u-r  t-i-m-e, make an i-n-f-o-r-m-e-d choice. Remember, you may have this system for at least 3 - 5 years.

If you're like me, you like seeing all your choices laid out in front of your eyes so you can see the big picture and make an informed choice. Use the PC/Laptop Comparison Check List spreadsheet below if you are computer shopping.