I dont think that it would be a good buy. Even though Koga is a decent brand, the bike is ancient and the parts are really outdated.

It also depends on what you want to do with the bike. If you want to cruise to the shops and back go out and get something plain and simple.
If you want to cycle around and get addicted to the sport (here's me holding thumbs!) then I would advise shopping around a bit more and getting something newer than that.
It will make a HUGE difference to your cycling pleasure.

As for buying second hand carbon bikes, I really dont think that it is that scary. If you dont know anything about bicycles then just take it into a local bike shop and ask for their opinion.