You have to find a way to make exercise fun or else you won't do it.  If you walk indoors on a treadmill, I recommend moving outdoors into the fresh air.  Some ways that people make walking fun are by:

• walking (and talking) with a good buddy
• using gadgets like pedometers and heart rate monitors
• challenging themselves with a goal, such as training to walk for a cause like breast cancer or leukemia
• following a walking fitness program that has actual assignments
• having a destination so you're not walking to nowhere
• walking in beautiful surroundings that change with the weather and seasons
• joining (or starting) a walking club
• playing games, such as a scavenger hunt

If none of these ideas sounds good, then switch to a different exercise because walking is not for you.