Retrieving function in vbscript

In my page_load event I want to run a vbscript that will return a certain file from the user's computer. My function finds the file all right, but how do I retrieve that file name in my ASP.Net code?

I'm doing the Page.RegisterStartupScript("FindFile",strScript)

where strScript is the vbscript. Now I want to load a textbox with the file name when the page renders. I can't say txtFile.Text = FindFile, because FindFile is not defined - I assume it already executed in the Register function.

Any ideas?

Thanks,
Larry