To setup USB storage in D-link 2750u please see this video.
To access your usb hard disk from PC please map network drive
and put this server address \\192.168.1.1\usb1
If you have partition in hard disk than type following server address
\\192.168.1.1\usb1_1 for first partition and for second partition
put \\192.168.1.1\usb1_2
For details see video
آی-ویدئو