Yes, you probably can replace the fork with a suspension fork, but may not want to for two reasons.

1- Suspension forks are taller than standard rigid forks to provide room for the travel. So, unless your current fork is a longer "suspension ready" model, the suspension fork will raise the front of your bike by 2-4 inches which will change it's handling characteristics.

2- Many low to mid-priced rigid mtn bikes weren't made for the kind of riding you're now doing, which is partly why your old fork isn't surviving. While a suspension fork might help, odds are that you'll ride that much more aggressively, and likely trash the frame next.

Consider taking advantage of the slow season, and dealers needs to clear out leftover 2010 bikes to shop for a new suspension bike suited to how you're now riding. It will cost you more than a fork, but then everything will be new, and quality coordinated for best performance. Later on you can find a replacement fork for your old wheels and keep it as a "B" bike, or commuter/utility wheels, or sell it used.