I had similar problems with Linked Reports. There is no property of "portrait" or "landscape". Everything is done by page size. See the following links to set and/or control page size:
http://blogs.msdn.com/bwelcker/archive/2005/09/07/461758.aspx
Also get RSScripter from SQLdbatips.com:
http://www.sqldbatips.com/showarticle.asp?ID=62