OnCommand 5.0 (a.k.a. DFM) uses the login credentials of the hosting operating system. For example, if you've installed OnCommand 5.0 on a Windows 2008 server, you would need to login to the OnCommand Console using a windows account that has administrator privileges (local or AD account). Once logged in, you can add other windows user accounts to OnCommand and assign roles to grant them privileges. Refer to the OnCommand 5.0 Administration Guide for more information.
If you're referring to OnCommand Report 1.0, the default login/password is admin/admin123.