You need to open them in objects maker first and then put them into a group. Object Maker (http://www.feral-heart.com/index.php?option=com_content&view=article&id=15&Itemid=25) or Objects in Map Maker (http://www.feral-heart.com/index.php?option=com_content&view=article&id=8&Itemid=12)
If you're still having trouble in object maker: Make sure you are placing everything into Feralheart >>> media > objects > my_objects. Also, when you type them in in object maker, you need to include the .mesh. So, if you mesh was named tree1, you need to type (in object maker) tree1.mesh. It is caps sensitive, from what I have heard!
(http://i62BannedImageSite/10nre4p.png)
First picture: Open your mesh. Second picture: Add you're mesh and make it's own group. Then you can add as many meshes as you want into that one group. I called my group "test."
(http://i57BannedImageSite/124vtxi.png)
Once you're done with that, go into map maker and add your meshes. :)
I figured it out, Thanks anyway!
No problem.~ ;) Good luck with your map.