Connecting like that will not give you access to the part of the filesystem that you need. Although you can do it in 2 parts:

1) Copy files onto N900 somewhere (anywhere) using either mass storage mode or pc suite.

2) On N900 open X terminal, become root and then move/copy the files to the correct location.


If you want direct access to the full filesystem from your PC then follow this thread:

Full file system access via both USB and network using OpenSSH + WinSCP