Hi, Bob,
As Victor replied, you can access it using BIDS (Business Intelligence Development Studio). Assuming your machine has the SQL Client tools installed, you'll find BIDS under Programs....SQL Server 2008.....
One thing...BIDS doesn't allow you to do very much with a DTSX package, unless you also create an Integration Services project in BIDS (which you can do by creating a new project and specifying the SSIS template) and then add the existing DTSX package to the project.
Additionally, you can use SQL Server Agent to create a scheduled job that will execute the package (unattended) on whatever schedule frequency you need (every night at midnight, every Friday night at 2 AM, etc.)
Hope that helps...