I have a multigym, punchbag and a cycling machine in my loft convertion, I use them 3 times a week for about an hour and vary what I do, since starting that 2 years ago I've dramaticly improved my strength, agility, stamina, and over all fitness, as well as my physical appearance. I also do a lot of mountain biking at weekends. I would say it's easy to get caught up in the right and wrong way to do things, but the bottom line is, it should be hard work, but you'll know when you're pushing too hard..
Tracy, woud be interested to see a before and after pic, respect to you!