the Snow Leopard installation disk.
However, I have seen many reports of the installation not going well and failing.
I think that Apple's original intention was for the end user to be on Leopard to begin with and then upgrade to Snow Leopard.
Still, @ $29 it is worth a try.
1. Install over Tiger. The clean install, also known as an Archive and Install, has gone the way of the dodo.
You will, of course, have a full backup of all your data, iTunes for instance, before you start.
Just insert the Snow Leopard disk and follow the instructions.
2. Increasing your RAM should help you. You may want to increase it to the max that your machine will take. You will find that information at Crucial.com.
3. You have not mentioned how much hard drive space you have available so I cannot advise you as to whether you should "clean out" your hard drive.
It is certainly possible to move your iTunes music to an external drive, in fact it is quite an easy move to make.
All you need is an external drive, something that you will be seriously thinking of getting to take advantage of the Time Machine backup that is part of OS X Leopard and above.
Hello folks

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic