Will leopard run on Mac OS X 10.4.11?

You can use Snow Leopard to upgrade your Mac with Tiger. Buy Snow Leopard > http://store.apple.com/us/product/MC573/mac-os-x-106-snow-leopard Then, make a backup, insert the DVD and upgrade. Finally, go to  > Software Update to install the most recent version

Snow Leopard = OS X 10.6.x

It is Not available as a download... It is a Paid Upgrade.

Do this first...

Check that your Mac meets the System Requirements for Snow Leopard...

Snow Leopard Tech Specs

http://support.apple.com/kb/SP575

If so... Purchase a Snow Leopard Install Disc...

http://store.apple.com/us/product/MC573Z/A/mac-os-x-106-snow-leopard

Other countries...

http://support.apple.com/kb/HE57

After the Successful Install, run Software Update to get the latest updates for Snow Leopard.

Be sure to make a Backup of your Current System Before Upgrading...