Mapping a network drive should still be available. Opening Explorer and going to one of the folders on the drive and right clicking should give you the option to Map the drive. I just did it on Windows 8 and the dialog box opened behind the Explorer Window..., but Windows 7 should be the same as it was before.
Is that not available? If so, have you changed anything on your network that has not been changed on the NAS?
From the question, am wondering what install you are asking the question about. Is it another Windows 7 install?