You can install it clean, regardless of what OS you are currently running since Snow Leopard is not Snow + Leopard; it is a full running OS. I recommend that you have at least 2GB RAM, and if you can max out higher than that, do it. I have 8GB in my MB Pro, but our other machine only has 3GB, but runs SL fine. Both are dual core Intel machines and is a requirement so that earlier models non-Intel based are out of luck, I believe.
I was in the same boat, with our desktop machine running TIGER, so I installed on a clean hard disk; I didn't UPGRADE. This way Snow Leopard didn't have to utilize current settings, etc..., I started from scratch and never had any problems.
Make a note of all your applications, settings, etc..., then insert the SL disk and restart and install fresh, deleting everything on your current disk. If you have Time Machine, or some ability to close your Tiger volume, DO IT. Just a smart thing to do.
Also, always have a backup startup volume externally, or internally if you have a second hard drive; after you see that SL works fine, you can replace your backup volume with the SL volume so that you can startup with the same settings and applications, etc... and keep moving. Update your backup volume once a month in case you add applications or change significant settings like where your iTunes library is located.
That should help.
hello mac heads...i am running TIGER in my MAC but i was thinking to upgrade to snow leopard,i wanted to know if do i just install snow leopard on top of tiger or do have to uninstall tiger then install snow leopard plus i heard that i need certain amount of ram to install snow leopd and where on my mac do look for how much ram i currently have and i do not want to lose my music on my itunes,thanks for your help.