A natural thing to want to do with a DTS package is to parameterize it so that, for example, it can work with different data sources/destinations than the ones it referenced when it was originally built. Things like global variable values, connection properties, object names, and the like are natural targets for parameterization.
There are a couple of ways to parameterize DTS packages. The first is to use a Dynamic Properties task. A Dynamic Properties task allows you to set the value of any property in a package from one of six sources:
A global variable from the package
A value in an INI file
An environment variable
A T-SQL query (only the first column of the first row in the query result set is used)
A data file
A constant ...