I might be wrong here, so feel free to correct me if I'm telling lies...
Are You sure that NTFS is supported? I presumed that NFS is the used partition type?
Have You tried to format the disk from within the DS' own interface?
EDIT: Sorry, just read you post more closely. You need to get the web-interface working first... *doh* My bad...
EDIT EDIT: Try disabling all firewalls on your PC if possible.
Both McAfee and Windows' own (if enabled).
McAfee caused me a few problems, and I ended up just using the bulit-in FW in Windows XP.