Does anybody know what the risks of inserting stents into blocked or
narrowing arteries are? Do the benefits outweigh these risks?

Hi,
Here are sites for patients on the subject:
http://www.manchesterheartcentre.org/textonly/txtangioplasty.htm
http://hcd2.bupa.co.uk/fact_sheets/html/coronary_angioplasty.html
http://www.guidant.com/webapp/emarketing/compass/comp.jsp?lev1=proc&lev2=stent

Don't be put off by the fact that in the first site more space is
spent detailing the risks, they have to listed and detailed, while the
benefits are just a few lines.  The alternative is usually open
surgery.

You can find many more using the search terms:  stent risks benefits

Some are them are difficult for a layman to comprehend.  As I
discovered, there are stents now that "elute" drugs.  The one article
I proused was questioning the practice  - or the choice of drugs.  You
might read it and ask your doctor his opinion  (maybe copy it and show
him).
http://www.acponline.org/journals/news/may06/periop.htm

We are all afraid of invasion of our body, and reading about the
processes doesn't necessarily reassure.  My second hand experience is
from playing tennis with persons who have stents  - and who have had
no problems.

Good luck