Rather than hidden files, isn't this likely to be a hidden partition - the one with the system backup/recovery files?
Not sure of all the keystrokes in Vista, but (using XP terms) if you go into control panel, administrative tools, computer management, disc management - or something like that - you can see all of the partitions including hidden ones.
Even when you find this, the disc will never actually hold 160Gb, partly due to formatting, and partly due to 1Gb in hard disc terms being 1,000,000,000 bytes but in binary terms being 1,073,741,824 bytes. So you will only get about 149 Gb on your '160Gb' disc.