Hey Sugar welcome to the stacks!
1. there's plenty of sites out there just google blackberry themes and you will find a ton.
2. You can use any MP3 and also edit them shorter for ringtones. Many people use the program Audacity for editing
3. Tetris I have no idea about, but BB Weather look here to get it to work http://blackberryforums.pinstack.com...work_81xx.html
Another good weather app/web page is http://m.wund.com/ it's great and accurate and has an animated radar.
4. check out this thread http://blackberryforums.pinstack.com..._all_apps.html
or the 3rd party apps forum.