Site Hacked

You need to start working your way through these resources:

http://codex.wordpress.org/FAQ_My_site_was_hacked

http://wordpress.org/support/topic/268083#post-1065779

http://smackdown.blogsblogsblogs.com/2008/06/24/how-to-completely-clean-your-hacked-wordpress-installation/

http://ottopress.com/2009/hacked-wordpress-backdoors/

Anything less will probably result in the hacker walking straight back into your site again.

Additional Resources:
Hardening WordPress

http://sitecheck.sucuri.net/scanner/

http://www.unmaskparasites.com/

http://blog.sucuri.net/2012/03/wordpress-understanding-its-true-vulnerability.html