Determine Calling Program

I need to write a VB Script or Batch file to open MS Word with a a document depending on which application opens the document. If its From IE i need one set of switches and everything else needs another.

The only way i've thought of to do this is the change the File Type to open all .doc's with a VB script instead of MSWord then have that VB script open word with the correct switches.

My question is, how do you determine which program called the VB Script?

Thanks,