To use the Ant cvs task, one needs to provide the password for the given CvsRoot.
Most CVS clients read the passwords from a file called ".cvspass" in the user's home directory.
The following Ant task stores the password for the given repository in the \${user.home}/.cvspass file:
<cvspass cvsroot=":pserver:username@machcvs:/cvs" password="password"/>
However, CVSNT ignores this file and uses the Windows registry instead. So you have to create the registry key HKEY_CURRENT_USER\Software\cvsnt\cvspass and place the new .cvspass entry there (as REG_SZ value).