You're not really giving us much to go on.
Why doesn't he want you to go on live? Has he explained his reasons to you?
If so, do you understand his reasons to the extent of being able to explain them to us, so we can either help you convince your dad or help you accept his reasoning?
It could be that he's got a really valid reason which you should accept, (e.g you have very limited bandwidth & he doesn't want you "hogging" it all for gaming as he needs to use the internet a lot as part of his job) or it could be his reasoning is completely unfounded & misinformed (e.g. another father told him that Al-Quaeda use COD4 as a recruitment tool & paedophiles can touch you through the headset with their e-peens).
Until we know his reasons why he doesn't want you to go on X-box Live there's not a lot we can do to help you.
My best advice is to sit down with him & ask him exactly why he doesn't want you to go on live, & if there's room for compromise, suggest using the free 1 month gold membership you get with live as a trial period, where he can observer what you're doing, then at the end of the month trial sit down & re-assess each others points of view.
But at the end of the day, he's your father & you should honour him & his decision, whatever the reasons, altruistic or not.