I don't want to be discouraging, but don't be totally shocked if you eventually end up with some foot/knee/leg/etc pain or other issues from running in a pair of walking shoes. Running shoes have more support/stability and are just shaped somewhat differently, to handle the different movement and higher impact when running.
I tried to run in cross-trainers a while back... ouch! I also wore out a pair of running shoes (by using them for other things, like tennis

) and started getting awful shin splints, even though the shoes *looked* fine. Shoes can make a big difference! Also, what your body could bounce back from in high school, it may not be able to anymore. (I know, it's been like 4 years based on the age in your profile, but there may be a difference.)
I'm sure that when you're starting out, a walking shoe will be fine, but once you're running longer distances you may want to invest in some running shoes.