Replicate DB2 table to SQL Server 2008
You could create a hidden timestamp column in DB2 on the replicated tables. When you run the replication job you can pull just the data that has changed since the last replication.  This would lower the quantity of data sent.

For instance, run the SSIS package every minute pulling just the last minutes worth of data. 

Or, instead of a timestamp field, you could use an auto incrementing int and keep a small table on the replicated instance that records the last int value replicated. The replication process would grab any new records, and update the small table's value to reflect the last value replicated.