SSRS function to get startdate and enddate when year and week numbers are passed

Hi, I am using SSRS 2008 R2 and passing Year, StartWeek, EndWeek as parameters and the report has 2 other parameters StartDate(Week) & EndDate(Week). Would like to default these parameter values accordingly. Report follows Monday through Sunday Week.

For instance:

@Year = 2012, @StartWeek = 51, @EndWeek = 52

Default values for @StartDate(Week) = '12/10/2012', @EndDate(Week) = '12/23/2012'.

Please help me achieve this functionality.

Thanks in advance............