Upgrading from v3 to v6

I find myself in a situation where I need to upgrade to v6 from v3 and I currently have Mac OSX 10.5.8. Looking at information on the website it appears that I can only update from v4 and above to 6. Does anyone know if there is a way of doing this without having to start from scratch. I appreciate that I will have to upgrade the OS too so I need to be pretty certain it will all work as I am not sure if v3 will work under 10.6 if I have to revert back.

Many thanks in advance for any help