Try this:
Select Project_Name, ReleaseDate, TaskName
From DB_Table
Where Project_Name like '{?Pm-?Proj_Name}'
And ReleaseDate >= currentdate
currentdate should be a valid database function or field to work. If you are using MS SQL Server, use GETDATE() instead.
If all you want is to filter records in a subreport based on a parameter from the main report, it might be easier to simply add the table to the subreport, and then create a Project_Name link between the main report and subreport. You can then use the Select Expert to filter the ReleaseDate as well.