If you want to create a gym at home then you will need to invest several hundred dollars.

The first thing you once you is to select or designate an area or room for your gym.  Whether it be the garage, basement, an extra bedroom the room should have plenty of ventilation as well as fans or some sort of cooling method.  You don't want your gym to be in a room that is warm or hot without some system to cool it.  Otherwise you can overheat during a workout session and faint or become severely dehydrated.

Another great suggestion is to have some sort of hospitality area, it could be a mini refrigerator or some sort of side table where you can store magazines, bottles of water, a stereo or anything else that will help keep you motivated while working out.

Media is very important when working out. 

You might want to consider putting a television into your workout room.  The television is not only great to watch during a workout session on a treadmill or bicycle or what ever fitness equipment that you have in your gym but it is also great for playing your workout DVDs should you choose to do a video instead of using a machine.

Music is probably one of the most motivational keys to use while working out. Music has a way of pushing you through an intense portion of the workout. An upbeat song can also help guide you into the rhythm or a pace for your workout. I highly suggest purchasing an iPod and a good pair of "running" headphones. Don't use the headphones that come with your iPod while you work out because those headphones are not designed to stay in place during vigorous activity. You'll want to create a workout playlist that features songs that will pump you up for your workout.

Deciding on your workout machines will be considered according to the amount of space available in your workout area and the cost of the machines. You could just get an all-in-one system such as the Bow flex but this is also very pricey. Piece of equipment will run you about $2700.

The Home Shopping Network have some pretty good deals on exercise equipment. You can purchase many fold up exercise machines that cost about $500.

You can also purchase some exercise balls, a yoga mat, workout DVDs and free weights relatively cheap.

Another source to purchasing equipment for your gym is to look on Craigslist or eBay. You can easily purchase used free weights and workout benches for very cheap. Just make sure that when you purchase them they are in good condition and not deteriorated.