This is a not a simple to answer, but here is theoretical how it should work. Or how will I do it.
I'll loop through all the files in the folder and, if the file has not been imported yet, do the import. You can easily find a code that will loop through files in a folder.
Create 2 tables first, tblC100 and tblC170 with a number of fields and field types that corresponds to TXT file fields.
Here you need some coding of the import procedure. It will go through files, line by line, and check either for "|C100|" or "|C170|" and write the data into the proper table splitting fields during import.
Also, once when completed, record a file name or/and with the date to avoid duplicate importing.
When you have data into 2 tables, there is no need to set any relations between them, you can easily relate them when you need to.
BTW you do not need manually to create a table. Create 2 text files and copy a single line with C100 into first and a single line with C170 into second and import them into the database using import wizard with text delimiter "|". Access will create tables for you.
Regards,
Branislav Mihaljev