Blocking Sites

Hi I made a small app over the weekend that allows one to block websites, I made this to block access to facebook
Now the method I am using is the HOSTS file in windows, this works perfect and blocks in all Broswers.
Now I know what you guys are thinking this can be easy undone your correct.

So my questions are
how to block sites?
Can this be done in VB.NET?
How?

I had two ideas one is a addon that filters IEs events I done this works fine but a problum not eveyone uses IE now
so you can get around with any other broswer.

Second Idea was some sort of proxy software between the client that fillters stuff before it's sent to the client.
agian this maybe ok but mean configing each broswer.

Any ideas.