We get this question almost every day so we ended up creating new FAQ for that

"We can run DTS Packages in SQL Server 2005/2008 without any problem so what's the need to upgrade them to SSIS?"
Well there are many good reasons why you should migrate DTS Packages to SSIS Packages very soon.

• Microsoft is going to discontinue support for SQL Server 2000 and DTS sooner or later so better you be prepared for migration now.
• SSIS has new many built in tasks which can save you significant amount of time compare to manual coding in DTS (e.g. Looping through files in a folder is inbuilt in SSIS - See Foreach Loop Container)
• Making package dynamic at runtime is easier using expression and configurations
• SSIS DataFlow engine is significant faster than DTS DataPump
• In memory transformations in DataFlow (e.g. JOIN, Split, Sort, Aggrigate, Union)
• DataViewer support to debug DataFlow
• Event Handlers support with separate control flow for each event
• ScriptTask in SSIS uses VB.net language with rich .net framework support. Script Task code is compiled so run much faster than DTS ActiveX script.
• Expression based control flow along with Success, Failure and Complete
• Reusable connection architecture

and ... many more....
For more information please download the following white paper
WhatsNewinSSIS.doc