The format for sp_executesql is:
exec sp_executeSQL @SQLString, @ParameterDeclaration, @Output = @Variable
Exact details in Books Online.
Without seeing what you're doing, that's about the best I can offer
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability