1rst Assembling your own PC is easy and there are multitudes of videos and help sites on the web to make it stress free. I help people at work through their first build on a regular basis and they never go back to off the shelf.
2nd set a budget, then ask for what you can do within that budget.
3rd what kind of games strategy, simulaiton or first person shooters determines how radical you have to get with the CPU and Graphics card.
Some pricing guidelines. Based on mail order or local as appropriate. Heavy sparts like case and pewer supply are best purchased locally. Memory, keyboards, mice, etc can usually be gotten locally at good prices. Video cards CPUs and motherboard go mail order for significant savings unless you have something like a Frye's locally. NOBODY sells video cards at reasonable prices locally.
Generic stuff:
Power supply - 500-600W* (Antec or enermax) $100-120
Case w/ 3 fans 2 in front 1 in back - $30-50-$200
Motherboard (MB)- $90-120
1-2 gig memory DDR or DDR2 depending on MB - $100-200
Critical choices:
CPU - $150-300, dual core or single won't matter. AMD 64 or Intel Core 2
Graphics Card - $200-400, Nvidia is the best bang for the buck right now. The 88xx series only since the older ones do not support DX10.
Personal Preference:
Keyboard - plain or with extra gaming keys
Mouse - optical with higher resolution
Monitor - size and type is up to you it will not affect performance unless you go for a cheap LCD which will blur in fast games.
Sound Card - not critical, on board is adequate if using speakers. If you want to drive his parents crazy go for the top end with 5 speakers
$25-200.
*If you go top end dual core CPU and dual Graphics a 600-650W will be required. Ask back here before buying. This is the most crtitcal component you will buy. If it is inadequate nothing will work right.
As stated above -
Avoid Vista for at least a year, it's too immature for the novice builder.
For a high end system build your own - cheap off the shelf is acheived by using minimalistic hardware (rot gut) and stuffing the system with spyware and bloatware that slows system performance. Off the shelf often does not supply full install and recovery disks which is critical for a high performance system. Off the shelf can not be upgraded due to the minimal approach on selecting hardware.
With all that said post back with some more details and we'll all be glad to help you spend your money in the most cost effective way possible. It is our favorite pass time here at OSNN.
Welcome to the boards.