Some routers can block websites/programs from getting on the internet. Most of the ones who can have the ablility to set it up for specific times of the day where you can't get on.
there is a program called winroute that acts as a firewall and has site blocking capabilities. (that costs though)
you could also use a proxy server and set it to block certain sites at certain times of day.
(in fact it's the proxy server part of winroute that does this. -we used it at a place I once worked at to block certain types of websites during the day, but opened access up at lunch times or the evening).
You are actually serious about blocking yourself from a site... alright.. Ah. I got nothing.. Just don't go to that site? It's not hard.. Just don't type it in. Saves you time possibly money and HDD space by not installing anything.