And once you have OS 10.6 you will need to update to 10.8 via the combo updater. Mac OS X 10.6.8 Update Combo v1.1
Perhaps you should first make sure your Mac is compatible.
Minimum specs for Snow Leopard. Mac OS X v10.6 Snow Leopard - Read the Technical Specifications2GB of memory might be the better option if your machine can accept Snow Leopard. You need the intel based version though.