from leopard to snow leopard on macbook

Backup your users folders to a external drive and disconnect first.

Make a note of all your installed programs, their serial codes, download locations and any other information, expect to have to wipe the drive as a last resort measure.

When you upgrade, stick the disk in and run the installer, it will take care the rest and reboot.

If the install fails (print out)

Simply hold c and boot off the 10.5 (yes 10.5) installer disk, second screen in is Disk Utility under the Utilities menu, select it and on your left is your hard drive name, select that and click Erase (format HFS+ journaled) , use the same hard drive name as before and Security Option Zero (optional) and Erase...

When done quit and then install OS X 10.5. When that's complete, reboot and go through the setup, use the same user name as before.

Once your in OS X again. stick the 10.6 disk in and install 10.6. Use the Combo Update here (better)

http://support.apple.com/kb/DL1399

Then install programs from fresh sources

Finally hook up the external drive. For each Music, Pictures, Movies, Documents etc folder on the external drive, select all the contents and copy to the same folder on the internal drive.

The logic in my steps explained

The reinstall of 10.5 give you your free iLife suite of programs that only comes on a OSX install disk with the computer. They are not present on the 10.6 retail disks.

The same hard drive name and user name, followed by the contents copy to the new respective folders on the internal drive ensures that all your links in iTunes, playlists and iPhoto works correctly as your matching the pathnames to the content exactly again.

If you get exclamation points in iTunes and your playlists don't work, then you'll know you missed something.