Answer to "Is it possible to waterproof iPod like 'swimman' do?"I have seen boxes that are made to water prof iPods. I would search the web first to see if it fit your price range. You always have the risk of braking some thing past what you can fix.
Answer to "You need to restart your computer? Randomly pops up. Why?"Ok I know this is an apple but this may help. In a PC there are restore points to restore your computer back to a time when you didn't have the problem. You have a ibook and what you have described is a virus apple does not get many virus made for them. Look for an antivirus program or try a disk boot-able LEX to get into your system, back up your files and redo the OS. Also don't give your ibook to your sister until she knows how to fix this. Ether she did this or let someone else do it. You have to work your computer like a gateway. Guard it or it will give away everything you tell it.