There's only one legitimate place I've found to watch it, the rest seem like scams :-/ You can watch it over here though: link
They make you do a little survey but after that it's good to go :)
Here's an awesome T4 giveaway:
link
Grand Prize is a hometown screening of Terminator Salvation for one winner and 200 of his/her friends (Before the movie's release!!)
If we're to believe director McG, the fourth installment of the Terminator franchise will be a gritty, dialogue-heavy, post-apocalyptic testament to Christian Bale.