Normally, each modification within a DTS package is committed as it's made. The Use transactions package property controls whether the package initiates a transaction when executed. And although this property defaults to true, you must also enable the Join transaction if present workflow property for a step in order to actually queue changes to a transaction. Since this workflow property is false by default, changes made within a package are normally committed as soon as they're made.
You can configure a package to log its changes in a transaction by:
Enabling the Use transactions package property (which is true by default) and
Enabling the Join transaction if present workflow property for each step that you want to participate ...