Actually the myth about running causing bad knees is very overblown. There really is no conclusive evidence to point to the fact running causes bad knees. Heres a few links to studies that show running does not lead to knee pain over anything else ...if you really want to read them.
http://www.pubmedcentral.nih.gov/art...?artid=2556152
http://www.ncbi.nlm.nih.gov/pubmed/18483739