I'm no expert in DTS, but I would assume that it will be using ODBC to access DB2, in which case you can use the TXNISOLATION keyword in db2cli.ini file
http://publib.boulder.ibm.com/infoce...d/r0008832.htm
the ini file will be under your sqllib directory.
Now, about what isolation level to use ... Well, what do you mean by 'data is being used all day' ... does it mean, read or write ... If it is read, you can use cursor stability, which will read only committed records and will not lock out the record for read by other applications ... Though, be cautious about using uncommitted read as this will capture all uncommitted records from the table also, which is likely not desirable ..
If the data of the exisiting records are changing, then it is a bit tricky .. it is not possible to suggest without knoiwing a) the type of data change and b) the criterion for rew selection for copy by DTS.
HTH
Sathyaram