Setting up a Virtual Private Network using a router running DD-WRT is easy. On a Buffalo router, start by navigating to /PPTP.asp in the web-based admin (Services/VPN). Click 'enable' on the VPN. At this point, some people might suggest pressing 'Apply Settings' at the bottom, but I was able to set all my parameters at once and then press 'Apply Settings.' The following settings worked for me:
Note the format of the 'CHAP secrets' section. This is important. And you might consider using trickier credentials, too :)
To set this up on OSX that's obviously outside your home network: in System Preferences/Network, Click the '+' to add a network, and choose VPN. Select PPTP as type, and use the default name or pick a new name for this connection and hit apply.
You'll be able to connect from this screen or from the icon in the top right corner. When you're connected you'll have the option of running all network data through this connection effectively using your home router as your Internet connection. This also gives you secure access to any computer on your home network via SSH, VNC/Screen Sharing, and I imagine AFP, too, but I've never tried it.