Do it Yourself computer kits are available for almost any type of computer you're aspiring to build.
Most DIY kits are referred to as "barebones" systems. A barebones kit is essentially a computer case,
power supply, motherboard, and sometimes cpu. The kit may also (but not often) come with memory (RAM),
a video card, and hard disk.
An operating system (such as Windows Vista) is almost never included. However, the actual components will vary from kit-to-kit.
Buying and assembling a barebones kit (or DIY PC Kit) is a great way to get started if you've never built your own computer before. A lot of the confusion that can result from buying incompatible parts is avoided, and, as a result, your experience becomes a more rewarding and enjoyable one.
A DIY or Barebones Kit's price can vary greatly depending on the features included. Some are designed for a modest home PC that may only be used for simple internet browsing and email. Othersare designed to give the builder a solid framework for building a very powerful and upgradeable gaming or high performance computing platform.
Here, you can find more information and prices on barebones computer kits
If you're interested in putting together your own kit, see my complete parts lists for a typical bargain or gaming pc.