Here is how it looks when you've selected a specific printer to format for:
The Paper Size menu lets you select create a custom size:
The dialog looks like this:
Applications can add a custom page to the dialog (the Settings dropdown is really a tab selector). These pages are from word:
(The last one actually looks like a standard page, but I haven't seen it in other apps)
Printer drivers can add extra pages to this dialog, and for postscript printers an extra page is generated from the UI description in the PPD file.
You can also have an inline preview widget:
Apps can also easily add their own custom page. Here is the one from Safari:
Word:
Keynote:
iPhoto:
Print preview is done by creating a pdf and launching the "preview" app which is the OSX pdf viewer. (Its in a special mode that adds a few buttons)
"Print Queue..." gives:
"Printer Setup..." gives: