Rather don't use the index tuning wizard. It's prone to giving rather sub-optimal suggestions. Learning to tune indexes yourself will get you much better results most of the time.
If you're not sure where to start, post the schema or one or two of your tables here, along with the more common queries and someone wll likly help you.
If you can, I would suggest getting a consultant in for a couple of days. Someone who specialises in performance tuning. They could then sho you how to go about things.
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)SQL In The Wild
: Discussions on DB performance with occasional diversions into recoverability
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