What computer to buy?

I haven't been following technology that closely so I'd like to have so suggestions as to what to buy. I'll be useing office programs and networking 3 or 4 computers and a printer together. The main computer will be the server . I'm on a budget $300-$400. I'll spend more on the main cp and less on the other 2. I'm looking at HP'S and amd and intel.

Please help!!
Brian