This article has some good points, but doesn't pick up on the critical one. If you really want to do this, there's no need to open up access to the machines on your home network. Set up two wireless routers, chain them, and connect your computers to the "inside" one. That way, the outside world can connect freely using your outbound internet connection (and public IP address), but your other machines aren't vulnerable to port scans on the open wifi channel. Since your internet connection is likely much slower than even the slowest wifi network, you can use a really cheap 802.11b router for the outside connection.