Ask HN: Whats the best way to learn networks (in particular VPNs)?

My last few attempts at setting up a VPN has make me realise that 1) This stuff is pretty complicated and 2) I have no idea what I am doing!

I really need to sit down and learn how to setup a secure and reliable network / VPN. What are the recommended books/sites/techniques?

Also by definition networks involve >1 machines. Is there an easy way to learn without having to rent a load of VPS boxes?