Valve and HTC are giving away developer kits of the HTC Vive VR HMD, but more than likely you won't get one. Only a select few will be chosen to receive a free development kit.
Signing up is as easy as going to the Steam page. Supplies will most likely be limited and unlike the Oculus Rift, not everyone will be able to just buy one. This signup is for serious developers only.
Now, the good news is that the consumer version is slated for later this year, so it shouldn't be too long before everyone can get their hands on one. That is, if there aren't any delays. It's not like Valve's known for delays, right? Right? Oh. *fingers crossed*