What is the full name for this login name?

With the native NET command:

    NET USER loginname /DOMAIN | FIND /I " name "

With (native) Windows Server 2003 commands:

    DSQUERY USER -samid *loginname* | DSGET USER -samid -display

Note:

The NET command may seem more universal, because it requires neither Active Directory nor Windows Server 2003 commands, but it is language dependent! For non-English Windows you may need to modify FIND's search string.