What resources do I need to home-build a VPN or VPN-like connection between a home-network (computer) and remote users. E.g., an Oracle/MySql/Access database at home and a DB user elsewhere.
Hamachi works with Macs too. I've set up a proxy using Hamachi on two Macs and Privoxy - works like a dream.
That all depends on your current network configuration including how you are connected to the Internet. If you are already using a router between your existing computer(s) and your modem, check to see if it supports VPN connections natively. Many routers already have this functionality built into them, you just need to configure and enable it. If that is not the case, update us here and we'll give you the gory details on how to build a VPN device yourself.
For a simple (afaik) Windows only VPN you can use Hamachi. http://hamachi.en.softonic.com/
Note that /all/ Himachi does is create a VPN connection between the VPN server and client. You then use standard Windows network shares and whatnot to actually do things like file sharing. Hamachi is so cool, that in most cases you don't even have to touch either sides firewall/router for port forwarding or anything like that. As a network admin, stopping Hamachi (even hoping to contain it) can be a pain in the ass, but as an end user it rocks hard.
BTW Hamachi is the backend software that LogMeIn uses if you ever used that service for remote desktop access.