htaccess Rewite Referer HELP!

[tip2tail]

Hi there,

I have 2 files, an exe and a zip located in my /software/ directory.
I want to have my server redirect requests to them to the a webpage
unless the request comes from my own site...

i.e. othersite.com links to mysite.com/software/app.exe and is
redirected to mysite.com/index.html

BUT

mysite.com/index.html is allowed to link to mysite.com/software/
app.exe and the user can download the file.

Can anyone help me?

Thanks,

Mark Young