Hi Louise,
Shin splints in a generic term for any pain in the shins and as such, isn't a very useful diagnosis for you. It very much depends on where the pain is as to exactly what the problem is. The website Bidders posted is useful and you might find this one helpful too...
http://www.sportsinjuryclinic.net/cybertherapist/front/lowerleg/shinsplints.htmBasically though, it is likely to be caused by one or more of the following.
1. Old trainers - have they done more than 500 miles or so? If so, get some new ones.
2. Change in training distances and intensities - have you increased your training distances and/or intensities too quickly? If so, rest the shins for a bit and build your fitness base in smaller increments.
3. Change in training surface - if you train only on hard surfaces (roads and pavements), you are more likely to suffer from shin splints. Try running on grass, trails or softer surfaces as much as possible.
Unfortuanately, there aren't really any stretches that you can do that will help the condition much.
Hope this helps. Good luck.
DW