I recommend the User folder trick.

Basically, what you want to keep is in your home folder right? Well there's an easy way to move over your home folder and retain everything perfectly.

Just install Leopard on a separate disk, or partition, or first back up your home folder. (/Users/yourname)

When you install Leopard create a user name that is different from your normal name. Now copy your Tiger home folder into /Users.

Then in System Preferences, create a new User with the same name as the Tiger home folder. OS X will ask you if it should use the existing folder - say yes and it will repair the permissions for you and you're good to go!