A few pointers for installing Web Deploy 3.0 onto an IIS7.5 server
1) Make sure that the Management Service has been added to the IIS Role before you start. Roles->Web Server->Role Services->Add Role Service (You'll need to scroll down the admin panel to see this.)
2) Don't use the Web Platform Installer to add WebDeploy to IIS7.5, its far safer to use the standalone installer from here: http://www.iis.net/downloads/microsoft/web-deploy#additionalDownloads
3) Use the custom installer option and make sure that the "IIS Deployment Hander" and "Management Services Delegation UI" options are selected.
note The installer won't proceed if your running in shared config mode
4) After install, you'll need to close and re-open the management interface, you should now have the "Management Service" and "Management Service Delegation" visible at server level within IIS Manager