Assuming you have the skill and temperament to install your own radiant floor heating system, it's something that can be done fairly easily if you take your time and do it right. As a very basic example of the steps involved in the installation of a hydronic system, we will assume you are working with new construction and a concrete slab.
The first thing to do is contact a custom radiant floor designer who can work with you to provide a pre-fabricated system. A pre-fabricated system is the best way to insure a hassle free installation, at least from the standpoint of hardware and other materials. There are plenty of companies that offer this service at a reasonable cost.
When you're ready to begin you'll first need to lay a vapor barrier down between the ground and your slab. If you plan to use insulation under the slab the vapor barrier needs to be underneath that insulation. With the insulation in place you'll then lay our your rebar in a grid pattern and tie it together using plastic ties. On top of the rebar goes the tubing for your heating system.
Running the tubing is where this gets tricky and where most problems occur. It helps to have two people doing this together; one to roll out the tube while the other one ties it off. As you run the tubing make sure to start where the room will be the coldest. This is usually the exterior wall furthest from the boiler. Run your tubing parallel to that wall, tying it to the rebar with plastic ties every 3 feet or so. NEVER use wire to tie the tubing and make sure your plastic ties are loose enough to prevent kinking.
When you get to the end of the wall bend the tubing around in a loop and begin a new line running parallel to the first. The two lines should be approximately twelve inches apart. Avoid tying the tube to the rebar at the loops as this will increase the likelihood of kinking during the pour.
As you go, be aware that in many places installing couplings below the concrete is a violation of building code due to the corrosive effect of concrete on brass couplings. Where a coupling is required, run the tubing out the end of the floor and install the coupling below the soil before running the tube back into the floor. Use the same process when moving from one room to the next.
Once the tube is in place all you'll need before the pour is an inspection. Some municipalities require a pressure test in order to pass while others don't. Once the pour is complete, all that remains is to connect your tubing to the boiler system. If you're using a custom system from a designer you should be provided with detailed instructions for this. A final inspection of your boiler system and you're ready to go.