Hi zarxto, welcome to the audio forum!
I am not sure what is your starting point here but I will assume you start with nothing but a computer. Like Silbereisen wrote, you will need a midi controller keyboard that you can hook up to your computer via USB, like this one for example:
http://www.thomann.de/gb/nektar_impact_lx49.htm(You can get cheaper or more expensive ones and you can choose to get some with more or less keys, depending on how you would like to play. This one is a good product that is in the mid-range price-wise.)
Then you will need a so called DAW (digital audio workstation). That is the programm you will be running to record your tracks and to host your 8-bit synth plugins. There are many options here, from Cubase to Logic (for Apple users) etc. Reason is fairly easy to use for beginners. Reaper is one of the best choices if you are on a budget:
http://www.reaper.fm/ (60$ for a discounted license). The other companies offer discounts and smaller beginner versions, too.
Now you can get to the meat of things, your 8bit synths. You can get those as vst-plugins for your DAW and there are plenty of them, many are freeware or don't cost much. Here is a small list of candidates (just scroll through the pictures and read the descriptions:
http://www.musicradar.com/news/tech/9-of-the-best-chiptune-vst-plug-ins-554428I hope this helped a bit. All the best for your 8bit-endevours!