Forum OpenACS Q&A: Response to Advice to ACS newbie wanting to do the problem sets, learn ACS

OS: RedHat 7.2 (because it's as good as anything else and most popular which means that you have the greatest chance to find the software/help from other people on the net).

If you're in Europe, I'd make that SuSE. At least at one point in time, they were outselling Windows in Germany.