I have a big problem opening http://localhost/ on Windows 7 (beta). I installed this os and everything went great; when I installed Wamp I saw that localhost is not working
I had the exact same issue, and the solution is what someone has already said:
In the taskbar, click on the WAMP icon.
Go to Apache-->Service-->Install Service
Then go back by clicking and selecting Apache-->Service-->Start/Resume Service
This will allow the localhost function to work (keep in mind I had already changed the host file located under c:\windows\system32\drivers\etc to remove the # from the 127.0.0.1 line)
If you need to edit that file still, you need to right click on it and select Properties. Then go to the Security tab, and click the Advanced button. You then need to select the Users, click Edit and select "Full Control". This will enable you to edit it.
That being said, you need to ALSO install the MySQL service following the same procedure.
MySQL-->Service-->Install Service
Then go back by right clicking yet again and selecting MySQL-->Service-->Start/Resume Service.
And that should fix it all up in Windows 7!