u can do virtual reality right now. www.asheronscall.com OR The Sims.
asheronscall does that all except without the helmet. you create a character with personalized features and u can change ur armor clothes weapons and much much more to make your character personalized then you can walk around and jump on stuff and fight people and wade through water and do many things. this is, a virtual reality. u interact with things that resemble real life and control a character that resembles you. ergo, VIRTUAL REALITY.
What you want is simply a virtual reality like asherons call in which you have a higher grasp on your environment. in asheronscall you can change the way your character is looking, but not by simply turning your head. thats what you want. virtual reality with greater ability to effect your environment.
and for what u want, u would need not only a helmet, but motion detectors, and sensors at your wrists, elbows, hips, chest, sholders, knees, and feet to tell the "virtual room" what u are doing. not just a helmet.
im sure u could do it right now, as they already have software that can handle it, for they make computer generate movies using such suits. but it would be like one of those 2 way webcams. they have their own software and ports and are not really part of the internet, but rather their own browser. unless u consider all things that use connections internet. but then your phone would be an internet browser too, wouldn't it? they would be an internet application if u could open simple html documents tho. mayby your browser could interpret it in a way that automatically made it move for you if you turned your head and mayby let you move your hand to click buttons instead of using a mouse.
you should indeed get your termanology right. makes things less confusing.