After completion of a "clean" install of Lion I get prompted for keychain passwords every 5 min. It's driving me crazy. I want my keychain to fill needed fields automatically as it had in the past. Most frequent is the "Microsoft_Intermediate_Certificates" prompt for Outlook 2011. I have searched all through Keychain Access and have found no solution. I even checked the box for keeping keychains unlocked and still it locks and prompts later.
Are you sure it's a keychain password and not just a standard administrator authentication?
It might be wise to run a permissions repair in Disk Utility or run Keychain First Aid from the application menu of Keychain Access.
In Keychain Access preferences, you can also elect to show the Keychain's status in the menubar to ensure that it's unlocked when it's supposed to be.
It's possible that you have more than one keychain and are being prompted to unlock older unused keychains. The two required keychains should be System and login--login is your personal keychain and should remain unlocked when you log in.
Also check to make sure everything is checked under Keychain Access Preferences->First Aid.