Of course you can upgrade your leopard installation to snow leopard, but i doubt u can boot it after that. Iatkos patches so many things that would be overwriten whe you install Snow leopard, leaving your system unstable and unbootable.
Instead, I recommend you a clean install using a Retail DVD. Thats because you only can install snow leopard using a retail dvd and u will have to install the bootloader and patch the kernel, kext manually.
Google or search this forum for a guide based on your AAO Model.
In 3 days, a completely turned off laptop discharges by 6%