More information on DSL should be available from your ISP.
First, make sure that your external hard drive is USB capable. If it uses firewire, then that might be the issue. If it is USB capable, then plug it into the powerbook. Wait at the most 1 minute for it to recognize the external hard drive. If it does not appear on the screen, you may want to try and plug it in on a second computer. If it doesn't show up on a second computer, the hard drive may have a problem/bug. If it does show up, then drag the selected files onto the hard drive. If it says you can't, then there probably isn't enough room on the hard drive to store the files. That is about all that can be explained to you from the information given.
Yes you can install snow leapord on to a mac mini, You would need a snow leapord install cd, You can buy one on the apple site
1. Right-click on the desktop and select Personalize.
2. Click the Change Desktop Icons entry in the left pane.
3. Check the Recycle Bin checkbox.
4. Click OK.
If the program is elsewhere it can be dragged into the application folder by clicking and holding the mouse button down on it's icon.
If the program is on a disc image (with a .dmg at the end of it's name - ProgramName.dmg) double click on the .dmg icon to launch an installer. Follow the prompts and the program will be automatically installed.