Here is another difference between DTS & SSIS that will trip you up if you are not expecting it. The issue deals with loading flat files with varying numbers of columns. For example the 1st row has 5 columns, then the 2d row has 3 columns, and then the 3d row has 4 columns. DTS handled this by always looking for the row delimiter first, whereas SSIS expects to always have the same number of column delimiters in each row. Here are some great posts that can explain this better than I can:
For some 3 years I worked in a shop that primarily did ETL work with DTS. I became quite familiar with all of the little quirks and idiosyncrasies of DTS, and I learned exactly how to get stuff done in DTS. DTS is like an old friend to me! But now I’ve started to work with SSIS – SQL Server Integration Services, the replacement for DTS that’s included with SQL Server 2005. The change to SSIS has been a challenge for me, particularly the separation of control flow from data flow. SSIS is vastly different from DTS, so if you have a need to start working with SSIS, do yourself a favor and budget some time to get up to speed. Believe me, you will need it!