You can use a gold subscription.

A LIVE account can be used on any Live platform, mobile device, Vista, Xbox, Xbox 360, etc. Basically, you can sign up for a gamertag on Xbox Live's website, and then go to your friends house, sign in on his 360, go back home, get on your PC, etc, etc.

Live is universal for it's platforms it pertains to.

Btw, when you get a 360, you'll have a 30 day free trial to Live, I do believe.