Not clear which version of Acrobat you are using: 10 (the type library) or 9 (you stated). To start with you should be using the Acrobat SDK relevant to your Acrobat product, but I can tell you that bookmarks have not changed. (Live documents for Acrobat X: http://help.adobe.com/livedocs/acrobat_sdk/10/Acrobat10_HTMLHelp/wwhelp/wwhimpl/js/html/ww help.htm?&accessible=true)
What API methods are you using to create the bookmarks? The IAC methods don't seem to include bookmark creation (on a quick check).