Since the release of the IBM PC, there has been a debate over prefabricated machines (herein referred to as "OEM") and custom built machines. So which is better? The answer lies with you.
One very common misconception is that custom built machines are cheaper to build than OEM. This is no longer the case. In the 1990's, custom built machines could be had for considerably less than OEM. However, today the difference in cost is nominal.
Before you purchase your next computer, make a plan out what your budget is, and what you are going to use the computer for. If you are a general Internet user, surf the web, use IM and download music, the odds are you'll just need a basic system. Any AMD Sempron 2400+ or higher or Intel Celeron 2.4GHz or higher will be more than adequate for that task.
If you are a gamer, I highly advise you build your own system or have one built for you. The reason being, there is a very small amount of OEM builders who use AMD chips in their systems. For gaming, you want AMD, there is no if ands or buts about it. For the best gaming experience you want an AMD Athlon XP 3200+ or higher or an AMD Athlon 64. Any of the AMD Athlon 64 series will be more than adequate.
There is another reason gamers should build their own systems — modification for LAN parties. No one wants to go to a LAN party with a plain beige tower, do they? No, they want cold cathode tubes and LEDs and clear windows on the side. If your going to be switching the tower your computer is in anyway, why void a perfectly good warranty? On a custom built machine, always save all of your receipts, because the odds are each individual part is covered by some form of a warranty.
If your primary objective is work at home, such as word processing, spreadsheets, database manipulation, desktop publishing, or anything of that sort, you'll want to go with an Intel processor. The Intel Pentium 4 is the right chip for data crunching, due to its larger cache size and deeper pipelining allow for more raw data processing to occur. You can find an Intel Pentium 4 chip in almost any OEM computer.
Another good idea, if you've never seen the inside of a computer tower, you probably would want to buy an OEM system, because custom built systems tend not to come with installation and configuration instructions.
If budget is your primary concern, it is important to know that AMD products tend to be less expensive than Intel products. Also realize that Sempron and Celeron processors are the inexpensive version of Athlons and Pentiums, so if performance is merely a secondary and you are looking to have a functional inexpensive system, go with a Sempron or Celeron.
So, if AMD Athlons are cheaper than Intel Pentiums, why are gaming systems so expensive? There are a lot of graphics cards and sound cards out there that actually cost more than your processor does. Remember that your CPU is only one component of your system.
At most computer shows and online computer hardware stores, you can pick up a combo pack of motherboard and CPU for a very good price, usually less than $200 — much less expensive than buying each individually.
Always keep in mind what your budget is and what you want to do with your system. Don't let others sell you on expanding your budget.