What are you trying to use the mesh for? Object maker/map maker, I presume? Here's a brief tutorial on how to install objects.
Download your objects! They'll most likely be in a file called a .zip. A .zip is simply a compressed folder. To open them, you need a program called either winzip or zip-7.
Once you download one of them, install it, and go to your .zip that you want to open. Click on it, and if it does not successfully open, right click on it and open it with your .zip opening program.
Then, you should see a folder with an object(s) in the zip-opening program. Your program will most likely have an option to "extract to" or "export to..." option. Select all of the objects and their .materials and picture images and export/COPY them to C: (C: drive, where most programs run on a PC) >> Feralheart >> media >> objects > my_objects. Done!
Go into object maker and type the name of your mesh in. You should see it pop up!
Here's a visual guide if you're confused on anything: http://feral-heart.com/index.php?option=com_jfusion&Itemid=2&jfile=index.php&topic=12012.0 (http://feral-heart.com/index.php?option=com_jfusion&Itemid=2&jfile=index.php&topic=12012.0)
I am trying to get some willow tree's for my map. I didn't put the names in object maker.... When I just did It told me the they could not be found... :-X
Where did you place the objects?
Also, make sure you places the object files in there, not the folder itself.