This will find and delete all duplicate rows. You can refine the granularity of uniqueness by including more columns than just the Primary Key. If you are picky about which rows you want to delete, don't use this. Instead use the 'Find Duplicates' script I just submitted and then delete manually.
When doing bulk data changes it may be beneficial to disable indexes prior to starting the operation. Fortunately, SQL's rich metadata makes this very easy to automate in a robust fashion.