3.0 files, can I restore?

The situation is the following:

- I have all the files of the 3.0 on my mac (using Snow Leopard, 3.0 is not working)
- I've just bought the 4.0 (not upgrade, full version)
- as i know, I can't upgrade (I bought an old mac, and there was installed a not registered version)

Can I restore the old files/programs under 4.0? (there are some important archive)

Any tip? Thanks!