1: The best OSes for PostgreSQLtend to be the free Unixes. This is because PostgreSQL uses a forking model, and both BSD and Linux kernels handle multiple process oriented programs better. That said, Afilias hosts the PostgreSQL database behind the .org and .info domains on big solaris boxes for the higher reliability of the OS there, and they just accept that they need more CPU horsepower to make it run well there.
2: The only time I've ever seen postgresql corrupt an index or a table was when the machine it was on had bad hardware (cpu, ram, hard drive).
However, until version 7.4 postgresql did suffer from index bloat when indexing monotonically increasing fields. I.e. you add 1000 records with max(id) +1 through 1000, and delete the first 1000 records. repeat over and over.
As of 7.4 this probelm has is taken care of with regular vacuuming.
3: 7.4 is quite stable, as are all the versions back through 7.0. However, generally speaking the later the version the better. The most commonly used is probably 7.2 or 7.3 however, since in production databases don't get updated to the new version just because it's out, especially if it's running well. I would recommend running 7.4
4: PostgreSQL can run on just about anything. I ran my first fairly good sized database on a P!00, later a dual PPro 200, and it ran fine. The things you want to spec for good performance, in order, are fast I/O subsystem, memory, and then CPU.
Once it's been downloaded, read the tuning document found here:
http://www.varlena.com/varlena/GeneralBits/Tidbits/perf.html
And join the pgsql-perform mailing list if you want some help with tuning later.
