To give a backward compatibility until the DTS packages are migrated(or converted by you) to SSIS packages, you can import the DTS packages into SQL Server 2005 and SQL Server 2008 and call them in the jobs to do their work.
These Imported packages will be present at the below location in SQL Server management Studio.
The DTS packages under this path cannot be edited in SQL Server 2005 and SQL Server 2008.
For editing these packages, you need to install "DTS Designer Components"
If you want to edit DTS packages in SQL Server 2005 go here, download and install the component "SQLServer2005_DTS.msi"
If you want to edit DTS packages in SQL Server 2008 go here, download and install the component "SQLServer2005_BC.msi"
Once you install the DTS Designer Components, it will allow you to edit the DTS packages as you do in SQL Server 2000.
Just right-click on the package and choose the option "open" and this will open up the DTS designer for you.
I strongly recommend to convert the DTS packages to the SSIS packages as the support to DTS will be completed removed in future versions of SQL Server.