C25K is amazing! I started that last year and will be running a half marathon in May...this from a girl who never ever thought she could run ONE mile.
I think if you've got an interest in running, you should check it out! As others have mentioned, getting actual running shoes - and being fitted for them at a running store - is really important. Also, take it sloooooooooooooow. Your body/joints are going to need to adjust to this activity, so go slow. That means don't run too much all at once, and also speed wise, take it slow. I often felt like people walked faster than I was running in the beginning, but that's okay! I'm still a slow runner today, but I'm faster than when I started
Also, if you're really worried about knee issues, you can build up some endurance by running in water.
Good luck in your running adventures!