For the most part having a large bandwidth will help with streaming, but like Takashi said, there are a lot of variables.
Your ISP could be limiting traffic on that particular port(s), other applications could be sucking bandwidth, etc.
Try turning off all network devices in your home, reboot your modem/router, and let it fully establish links again.
Once done, boot the Xbox and try to watch NetFlix. This may or may not solve the issue, but it's a good step.
This post has been edited by Ketchup_Bomb: Feb 3 2011, 01:10 AM