What is the best enterprise level PC auditing solution

I am looking for a solution that will allow us to audit our company's computer software and hardware nationwide. We currently have approximately 150 computers. 30 of these computers are inside the corporate network the rest are outside the corporate network. They connect to email via ssl over http but do not VPN into the corporate network. I need a solution that will allow us to continually audit all these machines and store the data in a centralized area that we can access at the corporate office. Additionally if possible I would like to be able to push updates to these computers as well. Any suggestions on software that is available, including open-source, would be greatly appreciated.