Price
Today, there are a wide array of hardware components and peripherals tailored
to fit every home computing need and budget. With all these options to choose
from, it can be a bit overwhelming if you’ve never bought computer parts before.
Shop around and remember to factor in shipping and handling, and taxes. Some
places may be priced a bit higher, but offer perks such as free shipping, limited
warranties, or 24-hour tech support. Many websites, such as CNET and ZDNet
offer comprehensive reviews, user ratings, and links to stores, including price
comparisons.
Since prices for any given part are always falling, its tempting to just wait
until the part you want goes down in price. Unfortunately the reason prices
decline is that better/faster parts are coming out all the time, so the part you
want this year that costs $500 may well be $200 next year, but by that time you
wont want it any more, youll want the new, better part that still costs $500.
At some point youve got to get on the bus and ride, even if the prices are still
falling.
Usually the best bet is to buy just behind the bleeding edge, where, typically,
you can get 90% of the performance of the top of the line part for 50% or 60%
of the price. That last 10% is very expensive and if you dont need it, you can
save a lot of money with the second-tier part.
It may well pay you to think of future upgradeability when selecting some
components. While the computer that you are building today may be fine
for your current needs you will probably need to upgrade it later. So look
for components that support the newest standards and have room for future
expansion, like a motherboard that will allow you to fit more memory than you
are planning to use, or a case that has room for extra hard drives. If your
current machine is maxed out the only possible upgrade is often another new
machine.
You may also find that by overspecifing in some areas you can save money
on others, e.g. if you don’t currently need fantastic sound but you do need
IEEE1394 (Firewire, iLink) then you might want to purchase a sound card
anyway as some of the higher end sound cards also have a IEEE1394 port.

Power
If money is no object, this is an easy question; just buy the most powerful
components you can find. If, like most of us, there are limits to what you
can/want to spend, then focus on those areas where more powerful parts will
pay off for you and scrimp on others. Always look for that sweet spot on the
price/performance curve where you get the most bang for your buck.