Download dialogs aren't really an easy task as you have to serve the users a page with the appropriate headers to classify it as a download. Otherwise by default it'll try to open which is fine unless you're serving PDF/Txt like documents. Best approach is to use jQuery and perform an ajax request for the download. I think there's actually a jQuery plugin for this making it even easier. Best results found simply with searching.

lmgtfy.com/?q=php+download+dialog

I'm trying to use the Joomla "PDF" function as a guide (I'm pushing a pdf file to the browser but need to do a couple of other things too, like record the download &tc &tc.).

I see, in this case you'll need a custom download parser to handle this.

An example is having the file download.php placed somewhere (where downloads stored?) and call that file with parameters (www.example.com/downloads.php?file=123.zip) then parse the parameters and obtain that specified file. In downloads.php you'd handle the headers to classify it as a download as well as handle the queries to log the click/download, etc..

I honestly believe you're better off using an extension like Docman to serve your downloads, why re-invent the wheel when 1 click away you've download management? Docman has grouping based permissions so it'd be easy to limit who can download what based off those groups.

("lmgtfy"? ROFL! I'd not seen that before : )

It's quite handy, many folks forget to Google before posting.. very helpful thing Google is.

I haven't found anything that allows me control at the file level easily. I haven't looked very hard at DocMan, it's true. However, then I want to stamp the PDF files according to who downloads them. I want to keep track of who downloads files and how often. Neither of these are particularly hard, they are all done. It's just getting Joomla and download links sorted out.

Docman offers downloads as well as logging who downloaded what via Download Logs and Statistics. Everything you're wanting/needing is already available in a download extension. If still wanting to use custom integration can offer best of luck but beyond that there's nothing I can do, sorry. Without the headers being set correctly the file will not be seen as a download through browsers.