Clean up > Optimize > Upgrade to Snow Leopard

Hey folks,
Once again sorry for the barage of stupid questions!

I'm currently doing a complete file back up onto an external courtesy of SuperDuper!

Is there any programs, that I can use to clean up odds and ends that aren't required by anything, and just optimize the system prior to upgrading.

I bought the Snow Leopard pack for £25 in PC world by me, but am slightly worried as I can't see a license key or anything? Do I need a license key for upgrades?

When I install this new operating system, what programs from Tiger that were previously installed will still be there/work?

As you can tell I have little experience on macs

Cheers,
Alex.

Once you have SL installed you will have all the basics Apps that it needs, so then you can connect the Ext HD and use Migration Assistant in SL to import your User data - Just don't import any Apps but download fresh SL friendly 3rd party Apps.