1. Some say it is better to do a clean install. But the truth is that an upgrade is as good as a clean install.
2. No, iLife 08 isn't included with Leopard. If you do an upgrade, iLife 06 would be there. If you make a Erase and Install, you'll have to install iLife 06 from your Tiger DVD, if you make Archive and Install, iLife 06 would still be there.