If this is a First Computers or you need to buy an operating system you may want to buy all OR MOST of the parts from one place to get the operating system at a lower price. Usually to get the operating system cheaper you have to buy a case, Hard drive, memory, motherboard and floppy.
Shop around a bit go look at sites like DELL and use a Custom System Selector and see what the prices are for the specific items.
Compare the prices at places like tigerdirect.com(Chicago I think), and computers4sure.com (California), Try looking at prices at Best Buy; they sell complete computer systems and some peripherals like Video cards, printers, Monitors, ect.
Sometimes a big store has good prices on monitors, printers, and video cards. I wouldn't want to pay the shipping on a monitor!
I bought most of my last computer from
(Cincinatti, Ohio). They let you customize a system, or order the Case, Motherboard, and CPU allready assembled; called a bare bones model.
I used an Enlight Case, which seems to be a pretty nice case. You can take the sides off, and the front panel comes off also.
Like other people have said, get a good power supply with the case both Pentium 4 and AMD Athlons have special power requirements. They require a steady rate of sustained power in a specific wattage range.
Cooling is critical. The AMD Athlons tend to run from 90 to 145 degrees F.
A good Video card is a good idea. Unless you never buy games or want to look at graphics, dont skimp too much on a video card. Nvida GFORCE2 is a good middle of the road model. If you are cheap maybe a 8 Meg Video card will do. There will just be some games that wont play on it. I am using a Raedon VE 32 MB DDR made by ATI. The Drivers arent as good as the GFORCE, from what I have been told.
Custom build shops are overworked at Christmas time and that can cause part outages and longer waiting periods for delivery. Look for the specials around Christmas, but make sure you are getting what you want and not what hasn't been selling well!!!
You may want to try some of those new molded Hard Drive cables instead of the flat ones that are about 2 1/2" wide and stop the airflow. Places like
sells all kinds of cables.
USB Devices are getting popular too. Stuff like cameras, printers, scanners, CDROM burners. If you do not like my post feel free to point out your opinion or my errors.