What kind of result do you get on an internet speed test such as
Speedtest.net - The Global Broadband Speed Test ?
Note there is a quality/bandwidth setting on the netflix web site under your account settings. You might want to try notching that down and see if it helps. I'm not sure how well their system auto-detects throughput and changes the quality setting, or if it even does that at all. (Hulu for example has an auto quality mode.)