Computer Performance Tips
Given all the components in a computer system, it's sometimes difficult to know which to focus your attention (and money) on when looking for the best performance out of a system.
My preference is as follows:
RAM/Memory - if you don't have enough, then the system will page to disk which is very slow. I generally would purchase the fastest memory that a computer will support, and would go with Dual-Channel over Single-Channel if possible. More is better than less - 512 MB of RAM is the absolute minimum that I would run on any modern hardware.
GPU - this wasn't really a significant factor before Vista came out, but certainly is now. Upgrading your GPU makes a *huge* difference when working with Vista.
Disk - Without looking at low-level parameters, there are three main things I would focus on:
RAID - whether disk will be striped (RAID-0)
Type of connection - i.e. SATA, SCSI, P-ATA/IDE
Rotational speed of disk - i.e. 15k, 10k, 7200, 5400 RPM
CPU - I find CPU is the least significant aspect of a system - more CPU is better than less, I generally go with 64 bit systems and single-core over dual-core at present.
Depending on the use of the system, a good graphics card with lots of fast memory and a high-capacity connection to the mainboard (i.e. PCI-X) might be a good purchase.
For motherboards, I exclusively work with ASUS.
For network cards, I work with D-Link unless I have a specific reason otherwise.
I go with AMD over Intel for CPU.