Read this excellent CodeProject article
Howto: (Almost) Everything In Active Directory via C#
There is a section "Create User Account" and "Dealing with User Passwords".
UPDATE:
To adapt the code for local accounts replace the respective lines with these:
DirectoryEntry localMachine = new DirectoryEntry("WinNT://" +
Environment.MachineName);
DirectoryEntry newUser = localMachine.Children.Add("localuser", "user");
Here starts the original code snippet for domain accounts:
public string CreateUserAccount(string ldapPath, string userName,
string userPassword)
{
try
{
string oGUID = string.Empty;
string connectionPrefix = "LDAP://" + ldapPath;
DirectoryEntry dirEntry = new DirectoryEntry(connectionPrefix);
DirectoryEntry newUser = dirEntry.Children.Add
("CN=" + userName, "user");
newUser.Properties["samAccountName"].Value = userName;
int val = (int)newUser.Properties["userAccountControl"].Value;
newUser.Properties["userAccountControl"].Value = val | 0x10000;
newUser.CommitChanges();
oGUID = newUser.Guid.ToString();
newUser.Invoke("SetPassword", new object[] { userPassword });
newUser.CommitChanges();
dirEntry.Close();
newUser.Close();
}
catch (System.DirectoryServices.DirectoryServicesCOMException E)
{
//DoSomethingwith --> E.Message.ToString();
}
return oGUID;
}
There are some specifics to understand
when dealing with user passwords and
boundaries around passwords such as
forcing a user to change their
password on the next logon, denying
the user the right to change their own
passwords, setting passwords to never
expire, to when to expire, and these
tasks can be accomplished using
UserAccountControl flags that are
demonstrated in the proceeding
sections.
Please refer to this great
MSDN article: Managing User Passwords
for examples and documentation
regarding these features.
CONST HEX
------------------------------------------
SCRIPT 0x0001
ACCOUNTDISABLE 0x0002
HOMEDIR_REQUIRED 0x0008
LOCKOUT 0x0010
PASSWD_NOTREQD 0x0020
PASSWD_CANT_CHANGE 0x0040
ENCRYPTED_TEXT_PWD_ALLOWED 0x0080
TEMP_DUPLICATE_ACCOUNT 0x0100
NORMAL_ACCOUNT 0x0200
INTERDOMAIN_TRUST_ACCOUNT 0x0800
WORKSTATION_TRUST_ACCOUNT 0x1000
SERVER_TRUST_ACCOUNT 0x2000
DONT_EXPIRE_PASSWORD 0x10000
MNS_LOGON_ACCOUNT 0x20000
SMARTCARD_REQUIRED 0x40000
TRUSTED_FOR_DELEGATION 0x80000
NOT_DELEGATED 0x100000
USE_DES_KEY_ONLY 0x200000
DONT_REQ_PREAUTH 0x400000
PASSWORD_EXPIRED 0x800000
TRUSTED_TO_AUTH_FOR_DELEGATION 0x1000000