Hi!
the basic feature set of the type-ahead search is available with NW 7.40 SP4 and SAP GUI 7.30 PL6. However, in order to activate the type-ahead on the dynpro side, you need the method cl_dsh_dynpro_properties=>enable_type_ahead() in a PBO module if you are running a NW 7.4 SP lower than 6. So, the example program provided by Peter should exactly do the job.
Nevertheless, as there are quite some bugfixes in the higher NW SPs and SAP GUI PLs, I recommend to upgrade at least the SAP GUI to the most recent one, maybe this already solves the issue. Moreover, on NW side there are significant improvements with SP5 and especially SP6. Please also see SAP Note 1861491 for details.
If nothing helps, please open a message on component BC-DWB-DIC-F4, so that we can have a look at your coding.
Best regards, Sebastian