The botulism spores are heat tolerant, that's why the higher heat of pressure canning is needed for low acid foods. But the toxin breaks down readily when heated to normal cooking temperatures. Here's a few links, google found many.
Journal of the American Medical Association:
http://jama.ama-assn.org/cgi/content/full/285/8/1059
The toxin is readily inactivated by heat (85°C for 5 minutes).
http://edis.ifas.ufl.edu/FS104
While the botulinum spores are heat stable, the toxin itself is heat-labile, so heating a food to 176°F for 10 minutes before consumption can greatly reduce the risk of illness.
http://www.medterms.com/script/main/art.asp?articlekey=25769
The toxin is heat labile and can be destroyed if heated at 80°C for 10 minutes or longer.
