How can I transfer files from and to the RWTH Compute Cluster?
You can mount your local drives into your RDP Session at connection time using the remote desktop connection program as described  here.
 Is the HPCWORK filesystem available on windows ?

Due to technical restrictions, unfortunately not.

 How can I view my QUOTA usage on windows?

Open the "Command prompt" from the start menu and type "quota".

Please note:

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The free space values you see in the drive properties using the windows explorer are NOT correct.