Welcome to CB! You can go to themes4bb.com, then go to forums then 8100 themes. They're free and if you want to download it directly to your phone make sure you use OTA (over the air) then you go to settings then themes! If you have anymore questions don't hesitate to ask. Hope this helped!
Zedge.com has free stuff for BBs nice wallpapers did not check out the themes but its got em. And if your new to your BB you might need to restart the BB by pulling the battery make sure everything is saved.
Posted from my CrackBerry at wapforums.crackberry.com
You can also look here on this site under Media Cornor, choose your flavor BB and look at what is available some of them are OTA ( Over the Air) I think I just downloaded one from themes4bb.com which was mentioned in a previous post. You can also get lots of nice ring tones and message sounds on this site go check it out and welcome to CB.