Agreed with the above. To get some good opinions, you need to share some details. What’s your price range? Where do you live? What’s your fitness level and age like? How long do you want the bike to last?
Most of us in the MTB world (that’s “MounTain Bike”) started on something just like that – an old hand-me-down bike with V-brakes, weak shocks, and a frame that didn’t fit. But as Ziphead said, the more fun you have, the more you’ll want to get into riding. A few hundred bucks can land you a great used bike, and let’s face it: we’re talking about fun and safety, so spend the money.
Check out your local bike shop (LBS) and see what they have. The Singletracks.com forum is a great place to find info from riders all over the US (and the world!), but it’s also worth seeking out local bike clubs that will know your local terrain better.