If you spend more than $250 "publishing" political speech online, counting hardware and software used, you must disclose your identity and register with the federal government. If you spend more than $1000, you must file as a Political Action Committee. Thus sayeth the Federal Election Commission.
http://www.aclu.org/news/1999/n101399b.html
http://www.aclu.org/news/1999/n101399b.html