Technicalities: 1

This is a guide on building the first kind of computer for a certain purpose of usage. In case you're just looking for enough to let you read/write MS Office documents, browse websites, check your e-mail, read blogs, etc., then this is your kind of build. Note that there is no graphics or sound card suggestion, because in this case, the motherboard chipset and built-in sound chip will be enough for what you will be demanding from your computer. Of course more is always better, but we're trying to go for an acceptable minimum, and buying hardware is most of the time the way to go for mounting a cheap computer with exactly what you want. So here's my suggestion for parts in the market for this computer (for AMD or Intel builds*):

Motherboard

Asus M2N68-AM Plus (AMD build)

Asus M4N68T-M (Intel build)

both are easily found in Europe at around 45€

...

CPU

AMD Athlon X2 6000+ (AMD build)

Intel Core 2 Duo E6300 (Intel build)

both are found for around 70€ in Europe

...

RAM Memory

Kingston PC6400 2Gb DDR2

should cost around 30€

...

Storage

Samsung 250Gb 7200 RPM S-ATA2 8Mb

found at about 40€

...

Optical Drive

LG GH22NS50 (or any other that has dvd read and write functions)

...

Operating System

I recommend Microsoft's Windows 7 Home Basic or Home Premium

As an alternative, Windows XP Professional should be enough

...

Peripherals

Any USB mouse/keyboard configuration (I suggest that you keep in mind ergonomics and durability)

(USB is faster and more flexible, but if you have few USB ports, use PS2 options for mouse and keyboard)

A screen (TFT or LCD preferably) with a resolution of at least 1024x768 pixels

A printer should be part of your basic office investments too, but I won't cover that market area

...

Case

Any simple ATX format case that includes a power supply will do just fine

*Note: the difference between AMD and Intel builds is only a matter of taste, at this point. It depends on what you have experienced before and prefer. Both are good platforms, and both offer similar prices in this quality range.