http://www.craigslist.org/about/domain_tou_violation
they say in the tos they don't allow that, there are some apps available though.
a lot of the software that i found via google charged money for a download and further reviews said they didnt work or were scams, etc.
here is one you can look into:
http://www.thecraigslistautoposter.com/
another one seems to be ezadsuite but their site seems to be down
http://www.ezadsuite.com