The first thing is to remember not to panic! I also assume you are on a Intel machine and not a PPC Mac so follow these steps:
1. Visit the site
Snow Leopard Compatibility to make sure your applications are up to date.
Optional:
AppFresh.
2. Get an external hard drive and use
Carbon Copy Cloner.
Optional: If you used Boot Camp use
WinClone to clone your Windows partition.
3. So clone your running Mac right now because we are going to clear out the junk throughout your Mac.
4. Buy a full copy of Snow Leopard
Snow Leopard Box Set so you can get the full iLife experience since you are coming from Tiger (10.4.x)
5. Install Snow Leopard but before the install program gets going use the Snow Leopard DVD to totally erase your Mac partition and do a totally fresh install. This way you will totally clean out the old data that will slow your Mac down. During the install process the Snow Leopard Migration Assistant (/Applications/Utilities/Migration Assistant) will come up and you can point ti to you clone to import you email, pictures. music, etc.). You will need to get a coffee or tea during this part because it will take a while!. After all the data is imported and the install happens use Software Update to bring you Mac up to 10.6.2. Then use the
AppFresh program to update your third party programs for Snow Leopard.
6. Use the iLife & iWork DVDs and install them then after that do another software Update to make sure it gets the updates for those programs from Apple.
7. Keep you tiger clone for a couple of weeks to make sure you get all the data you need from this clones.
Warning: Only fresh install the OS X partition, not the Windows partition!!!
Lastly I linked the
Snow Leopard Box Set because going from Tiger the standard upgrade disk will not work right going from Tiger and to give you the full Mac experience. Now there are ways to
do a fresh install with the SL upgrade disk. So if you don't want to pay for the Box Set then you can use just the
Standard SL OS X disk and forgo the iLife experience and substitute it is the above steps instead.