Doing a google search for "houses for rent in Hochiminh" will produce plenty. Some of the things you may run into are minimum one year lease, people asking for three months rent in advance, they will ask you to sign two different leases, one is your agreement with the owner, the other is a fake agreement that they put on record with the police that shows a rental price of half the real agreement. Many houses listed are for sale and may be sold without any notice. Most houses are originally built for no air conditioning.