I currently have a small office to small office IPSec connection that's been working very well. It's just two old 333 Mhz boxes that are running IPCop on them. I've had some problems, but it's mainly because one of the offices has a terrible internet connection. I've had more reliable dialup.

If you get a couple machines with a bit more horsepower you can mod the IPCop install to have all sorts of nifty features. It's just a suggestion, I've had decent luck with it.