Yes there will be a season 7, there are even a few spoilers roaming the internet about it. Desperate Housewives is locked in to an 8 Jahr contract (8 seasons). Though Marc kirsche the excecutive producer is trying to push it to 9 seasons oder even farther. Though so far it's on and it's not going anywhere. :)
there was an interview somewhere on Fanpop where marc kirsche sagte he planned to end at season 7 something and now the producers want him to extend it