Buying a computer system/Buying a PC
I am looking for a good gaming PC which won't hopefully go out of date in 5 years time. Trouble is that I have little idea of what the modern specs mean, these days. For example, what RAM do I need to still be able to play then-current games 5 years on etc. Any advice most welcome. I can't afford more than about 1000-1,250 euros from the german amazon branch for PC plus monitor.
Oh, yes, do I need these 3_D monitors that are sometimes mentioned?
Generally speaking "future proof" and similar concepts are impossible to achieve in practice; five years is an exceptionally long period of time to expect a machine to stay current for videogaming. A more realistic figure would be around 18 months, at which point you will likely be considering hardware upgrades (not total replacement though). However, this has to be considered in context: if you have a specific game that you like playing today, and buy a computer that can play that game, nothing will change that machine's ability over time (so you're really only up against when the hardware inevitably fails; a properly maintained and built machine can last for decades though).
My advice would be to figure out which titles you'd like to play, and see what the system requirements look like for those titles. That will give you an idea of what kinds of specifications your new machine should have. This will help guide your purchasing. If you have a few titles in mind, we can start from there in terms of what hardware would make a suitable machine.
Another suggestion would be to look into a gaming console - which will play any game released for it for the life of the console, and cost considerably less than a gaming machine. If you decide to go this route, I would also suggest waiting for the new generation hardware to release. The only caveat to this choice is that if the games you'd like to play (generally MMOs and strategy type games) don't exist on a console; the upside is that those titles are generally easier to run on a gaming computer (for example, World of Warcraft has substantially lower system requirements than does something like Call of Duty, but World of Warcraft is only available for PCs, while Call of Duty can be had for Xbox or PlayStation).
Regarding 3D monitors - no, you do not need one. It's simply an extra "feature" that you can integrate into a system; given your relatively small budget, I'd probably suggest passing on this feature now (a quality 3D monitor costs a few hundred US to start, and requires additional hardware to fully deploy).