Using ExpanDrive on windows is almost too easy
And it works on Win7 x64.

You can get demo from here.

1. Install it
2. Be sure that your N900 is connected to your wifi and that you installed OpenSSH Server on it
3. After installation you will get this window. Enter your details.

Drive Name: custom (e.g. N900)
Server: 192.168.x.x (install myip widget)
Username: root
Password: your password that you entered when you installed OpenSSH
Directory: I selected show only and entered "/home/user/MyDocs"

That is all the info I had to enter.

4. Click connect and you will see your N900 in windows explorer