I did a quick google and at least the HP desktop should have worked without problems.

http://blog.frith.co.za/2009/03/19/ubuntu-on-an-hp-compaq-dx2300-microtower/

The reason that a lot of people drop Linux is because it is different from Windows. Many people have taken a long time to the point where they understand the most common quirks with Windows. This may be a moving target, but it is generally incremental. Then they come to Linux, which has completely different quirks. As with anything new, there is a learning curve involved. The point with Linux though is that once you know how to administer a Linux system, then you can forget having to reimage and fool around with the system to keep it running. A running Linux system is stable, reliable and puts MSCE's out of work, hence the paranoia.

Ian