If you search back through the UT using terms such as 'PageSetupDlg', or even look in the MSDN online pages using this term, you'll find a number of references. I suggest you also look at www.news2news.com where you'll find a number of methods for accessing Windows API functions.

I had a lot of (bad) experiences doing this about a year ago... If you can possibly avoid the requirement for knowing the top margin, I suggest you do that.

HTH,
Simon