EFS on workgroup network

[ROcHE]

I have a simple network at home (4 clients, xp pro + vista) + a simple file sharing server (xp pro).

I use the "server" for two things, mainly. Backup of the clients files + sharing some media files.

Some of the clients files are efs encrypted.

Is it possible to retain the encryption when the file is backed up on the server? I read conflicting information about this.