youtube is not locked unless you are trying to access it from a network that has a blocking policy. (An academic institution or workplace for example)
In either case, if you have valid reason to use it just ask the network administrator and he/she can unblock it for you.
If you are at work, I do not recommended that you try to negate your employer's network security by try to DIY this as it is often taken as Gross Misconduct and thus ground for dismissal.
Many academic institutions take it as disciplinary matter as well.
T, May 2009
