So You want to Upgrade
The Big U, erm or something. Upgrading PC's is one of those love-it/hate-it kind of things. The possibility to expand upon a 'base' PC by adding peripherals or newer/faster core components is what has kept the PC as a viable and flexible platform.

There are pitfalls however to this myriad of chips and cards. When upgrading you have to think about what I refer to as an upgrade path. Hardware manufacturers and the powers that be only build in so much of a buffer to improve a particular motherboard or platform. Differences from manufacturer to manufacturer and standard to standard can also become a bewildering mish-mash of acronyms and weird naming conventions. I'll touch upon some of the most common trouble areas and things that have to considered.

RAM
Now we're not talking about animals here, we're refering to Random Access Memory. Think of this as short term memory, or a scratchpad. Just in the way that we as humans can't think of HUGE things in one sitting, computers need to digest information in smaller chunks. RAM provides this short term memory chunk. Information is loaded into RAM, processed by the CPU and acted upon. The results could be calculating values, outputting information back to the hard drive or any number of operations. What most people forget is that if it's running (ie: a program is open) it's using up RAM. The general rule is that the more RAM you have the more you can have running. Keep in mind, as with CPU's this isn't a linear performance boost. Having two times the RAM doesn't mean you've got the ability to run twice as many programs. The key thing to keep in mind when buying RAM is that there are many flavors. Always check what "type" of RAM your motherboard has. The most common types nowadays are:  SDRAM (all but gone), DDR and RDRAM. DDR (Double Data Rate) and RDRAM (Rambus DRAM) are the two most widely found types of memory in PCs today. All things being equal DDR is a more cost effective type of RAM. When selecting what specific memory to use, check with your motherboard manufacturer.  They will dictate the "speed" of the RAM that can be loaded and the maximum amount.

CPU's
The brains of your PC (Central Processing Unit) are perhaps the most sensitive component and sometimes the most costly. There are currently two key players in the game (don't start flaming me Mac people I do realize there's the PowerPC [IBM/Motorola/Apple]). Intel which produces the Pentium processor family and AMD/Advanced Micro Devices which produces the Athlon. For the desktop consumer market these are the two names you'll hear most often. Currently there is a hotly contested debate regarding 'clock speed' vs. 'Performance Rating'

Intel has long stood by the convention of identifying their chips based on the clock speed (this is akin to identifying an engine in a car by the liter displacement). The higher the clock, the faster the chip. However what is often misleading is that while the 'clock' may be 2x's, 3x's or faster, it does not relate to a linear performance boost. In short going from a 1GHz chip to a 2GHz chip doesn't mean a 2x's increase in performance. Realizing this aspect of chip design AMD, whose chips architecture results in a more efficient chip at slower clockspeed. As a result AMD began designating chips according to a "relative performance rating". As a result whereas an Intel chip might be identified as Pentium 4 3.06 GHz, AMD suggests that it is latest chip an Athlon XP 3000 is approximately the same performance. The long-and-short of it is this. Each chip has it's strongsuit. AMD's Athlon processors are very cost effective, though they sometimes run hotter. Intel on the other hand is the established standard. Most of their chips are priced higher than their AMD counterparts. Both are well suited to certain tasks. AMD chips do great for gaming and benchmarks. Intel's chipset tends to be less finiky than some of their counterparts.

When upgrading a CPU you need to make sure that the motherboard you have or plan to buy will support the chip in question. As a rule, always check with the manufacturer of the board to confirm which chips are designed to be used with a particular board. When selecting the CPU itself, make VERY sure of the specifications. Clock speeds, "core" speeds and voltage are three key areas that must be noted. When in doubt inquire with the sales staff of the online retailer or local parts shop.


Video Cards
Now what kind of gamer would I be if I didn't discuss video cards. In the world of cinema and gaming there is no greater deciding factor than your video card. Like the CPU wars there are two key players. NVidia a strong up and comer which stormed onto the vid card market in the tail end of the 90's and ATI a rather established company that has been around since the early 90's. Since 1998 or so NVidia, like Intel has held the "speed" king rating. Now however the tide has turned. ATI's Radeon series (starting with the 9700 series) has taken back the King of the Hill title in the video card market. Neither card really has a "cost" edge at this point. At the highside ATI's high end card and NVidia's cost about $500, with more value oriented units as low as $100.