Have a look at DTSRun in books online. It describes how to run DTS packages and the various switches you need. Using this information, you can create a SQL Agent job to run your package.
In its simplest form, the command will look something like
DTSRUN /E /S servername /N "DTS Package Name"
The "servername" is the name of the server where the package is stored (assuming that the file is stored in SQL Server.
Cheers
Stephen