Jean,
You can take a look at a sample DDE spreadsheet available at ftp://www.dtniq.com/iq/ . Download the Sample IQFeed DDE with T&S.xls. It is based on a macro that isn't supported, and isn't very good. However, it may give you some ideas.
At this time there isn't a way to pull historical data into Excel from the IQ servers using DDE. With a DTN.IQ subscription you can use the T&S app to export data into Excel though.
A good place to visit is the XLTraders group on yahoo. These folks are high end Excel users who have written many apps with various datafeeds.
http://groups.yahoo.com/group/xltraders
Jay Froscheiser
DTN Market Access, LLC.