The documented way to copy files securely using SCP or SFTP is to use the scp task added in Ant 1.6. This task requires a library (jsch), which appears to work fine with SCP, but seems to mangle Windows file names under FTP (backslashes get removed).
I have since stumbled on another library called Maverick Ant, which is free but obfuscated. Maverick is said to be faster, have not tried it yet. See the Maverick Ant page
I use these files with freesshd as a task running on Windows computer for home use (we use Bitvise winsshd at work)