Getting add on scenery to work

I just acquired FS2004 with the hopes of making use of some of the great addon scenery. I have tried a few and think I followed the directions but can't get it to work. For example, I downloaded the New York Objects V3.0. I Unzipped it, copied the NYObjects directory under the addon directory under my flight sim install directory. I then go into settings upon startup and "Add Area". I restart FS and I do see the area NY Objects there (Prio 1). However, now the buildings that it is supposed to replace (e.g. World Financial Center) are completely gone! I also tried the New York Modern and I get no World Trade Center and, again, the World Financial Center is gone. I tried them separately and this happened (I also tries them together but not sure if one is supposed to take precedence).I also had problems with the Bear Mountain area and the NY Lakes. But the problems were that I was unable to extract the ZIP files at all! I am on WinXP Pro. I did NOT do an "OPEN" in IE. I did a SAVE and tried to extract.Any info would be appreciated.Bill Smith