OpenDialogbox -> multiple text files

Question

Hi basically im using a Opendialogbox control at the moment and I have the option to open a text file and send to the data base one at a time.
What want to do now is give the user the option to highlight multiple text files at once and send to the database all at once.

I did enable the openFileDialog1.Multiselect = true;

but when I highlight all or multiple text files, it only process one text file in the database or mdb and not all, can some one help me.

also in my mdb file there cant be no duplicate text files in the database, so how can I scan the database to check and see it the filename exist or not
.

If the filename exist skip, if it dont exist add to the  mdb. im try to all this once I multible textfiles at once then do the check while adding to the database.