Get checked as soon as possible.

Like Todd said, the color will tell you a lot. If its red, I would not be too concerned, although I'd still get checked.

A couple years ago my dad had black blood in his stool. Turned out it was a new medication affecting his ulcers.

I just recently had a colonoscopy and it was a breeze. The worst part was not eating real food for 30+ hours. That sucked!

Good luck.