I stand corrrected from the FAQ on xbox website for LIVE:
Q: Will I need some sort of "Xbox Live 360" membership in addition to my existing Xbox Live membership if I want to use the Xbox 360™ video game and entertainment system on Xbox Live?
A: No. The Xbox Live service you know and love supports both the original Xbox video game system and the Xbox 360 video game and entertainment system. Once you migrate your account information to your Xbox 360 console, you'll be all set for gaming on either system.
No question, Xbox 360 delivers the full force of our dramatic service improvements to Xbox Live, but the service you subscribe to is the same.