Yes, most definately, thanks for the reinforcement.

Thanks to all who replied, most helpful, keeping to my usual style I normally post what I ended up doing and why:

I've gone with the $ENV{PATH_INFO} idea, because the header stuff caused double prompts and general mess in IE, worked perfectly in Opera though.

However, I'm not actually using the $ENV{PATH_INFO} contents, I'm just calling the CGI in that style and passing the required info via post such as below, 'run' is the CGI and 'cda' is an ExecCGI-d directory:

<form method="POST" action="/cda/run/surtron-020130-03.zip">
<INPUT TYPE="image" src="/images/icon-zip.gif" ALT="Download surtron-0
+20130-03.zip" BORDER="0">
<input type="hidden" name="mode" value="download">
<input type="hidden" name="file" value="surtron-020130-03.zip">
</form>
[download]

This is almost a shortcut I guess, looks neat from the client side and works well in all cases. As long as I check for tainted posts it seems to do what I want.

Update:
I have now changed the above so that the filename hidden field passes a database id instead of the actual filename to make it less h4x0rable.