Computer Names:
• The computer name must be in uppercase 15 or fewer bytes long (depending on which characters are used and the language set as the Language for non-Unicode programs in Regional and Language Options in Control Panel). If your network is using a Microsoft DNS server, you can use any characters except periods.
• If your computer has TCP/IP networking installed, the computer name can be up to 63 bytes long (depending on which characters are used and the language set as the Language for non-Unicode programs in Regional and Language Options in Control Panel) but should only contain the numbers 0-9, the letters A-Z and a-z, and hyphens. You can use other characters, but doing so might prevent other users from finding your computer on the network.
Usernames:
• You can use up to 20 uppercase or lowercase characters to specify the name of the account, or up to 15+1+20 characters to specify a fully qualified domain user name of the form: domain\username. These forms are distinguished by the absence or presence of exactly one backslash (\) character.
• The following characters are prohibited: / \ [ ] : ; | = , + " * ? < >
• Also, a domain name cannot contain any spaces or start with a period. A user name cannot consist solely of periods and/or spaces.
Passwords:
As password complexity is the default in a Domain:
• Passwords must be at least six characters long.
• Passwords may not contain your SAM account name when it is three or more characters in length or any full "token" in your display name that is also three or more characters in length. For example: If your SAM account name is etiennej and your display name is Jacques, Etienne P., there will be three blocked "tokens": etiennej, Jacques and Etienne. The middle initial is less than three characters and is therefore not considered a "token". Subsets like etiennej1 and Jacque12$ will not be blocked.
• Passwords must contain characters from at least three of the following four classes

escription Examples
English upper case letters A, B, C, ... Z
English lower case letters a, b, c, ... z
Westernized Arabic numerals 0, 1, 2, ... 9
Non-alphanumeric ("special characters") Punctuation marks and other symbols. If your network is using a Microsoft DNS server, you can use any characters except periods.
• These requirements are hard-coded in the Passfilt.dll file and cannot be changed through the user interface or registry. If you want to change these requirements, you must write your own .dll and implement it.