First of all, DTS (and/or SSIS) packages are just that, packages. They can be saved to a code file, a proprietary file (.dts or .dtsx), or saved in the MSDB repository. When they are saved in the repository, they are stored as an IMAGE (or large binary) data type.
That is just storage. What the package does, how it executes, and the environment where it executes is up to you and the definitions within the package itself.
The tools outside of SQL Server help develop, deploy, and run the packages...regardless of where they are stored.
If you have restored a copy of an MSDB database from one platform or another, or exported out these image files and imported them to another system, you should still be able to read them with the native DTS, SSIS, BI Studio tools.
Keep in mind that SS2K packages are stored in MSDB.dbo.sysdtspackages, whereas SS2K5 packages are stored in MSDB.dbo.sysdtspackages90, and can only be read by the appropriate tools.
The SS2K5 tools can read SS2K packages, but only for execution, not for modification or upgrade.
Hope this helps.