As Jeremy stated, it's almost impossible to get the details to external files from inside TW due to the security restrictions of the Browsers.
One of my TW's makes extensive use of external files (.PDFs and images) and the only way I could get them integrated was with external batch files.
This is one of my import routines:
@echo off
cd Unsorted
for /f "Tokens=*" %%f in ('dir /l/b/a-d') do (rename "%%f" "%%f")
cd ..
FOR %%A in (Unsorted/*.pdf) DO (
echo ^<div title="%%~nA" modifier="Imported" created="201001011200" tags="Unsorted" changecount="1"^> >> entries.div
echo ^<pre^>^|!Name: ^|%%~nA ^| >> entries.div
echo ^|!Author: ^| ^| >> entries.div
echo ^|!Date: ^| ^| >> entries.div
echo [img[./Images/Book.png][./Documents/%%A]] >> entries.div
echo ^</pre^>^</div^> >> entries.div
)
It is designed for TWC and has a specific layout, but it may suit your needs. But what it does is first switch everything in the "Unsorted" sub-directory into lowercase (this prevents loads of error where it tries to wikify the names of the .PDFs that are imported) before building a file with all the names of the PDFs as tiddler titles. The resulting file (entries.div) is then placed inside the TW file. When I go through and edit all the "Unsorted" tagged entries, TW handles the tidying up of the actual tiddlers.