So, to second what Drew said--there's no way to control the buttons individually. But there's the exception that Open will appear, or not appear, depending on whether the browser recognizes your file type.
First, I haven't seen the "More" button you mention (running IE 7, XP Professional SP2).
Second, scouring the Web brought me no idea of how to control the buttons individually.
However, regarding Open, I noticed that a client OS that was not configured to recognize the file type being downloaded would not know which environment to open, and therefore would not display the "Open" button--for example, the client displayed the download-file name in the File Download Box but Windows did not seem to recognize .doc files, therefore Windows didn't open the file in Word and did not display the Open button, only Save and Cancel.
Also, I did find some C# code that purported to suppress the Open. VB.NET seemed to recognize the code without changes except dropping the final semicolon. It didn't do the job in my app that the author claimed it did in his, but here's the code:
