188935 Security expert needed

looking to find flaws and holes into my network. I don't believe it's secure enough and I don't think it's set up properly. I'm looking for an expert. not someone with minimal experience. I need detail information and guidedance. If flaws are discovered, I need detail info on how to make it better. The in-house server is Windows Server 2003 and Exchange server. Every pc on the network has it's own ip behind a firewall. I need to know if anyone can access any of those ip's via remote access. I also need to know if the firewall is secured enough. We also have laptops accessing our network with their own ip's and also behind a firewall.