A little research brought me this: File Extension .D01 Details. I assume the .D01 you're dealing with is a Tonline DB file (from above) That's what it is.

I suggets posting an example of this file. I think you've said it's a plain text file - as there is no in-built PHP parser you have to make your own, as you would with any other file format.

This would include a file_get_contents, then looping through each line to parse it into something you can manipulate easily, for example insert it into the database.

I had a brief look for parsing details but couldn't find much.