Hello!
Welcome, and to answer:
- You'll need Barbarian Invasion.
- It won't harm you computer, nor will it prevent you from playing RTW. If you are so excited you just start to pee in your pants, the spill might get to your computer's connections, then yes, it might harm your computer (just saying, cause that's what it'll do to me, I'm just doomed...).
- No, only if it's made by douchebags.
- Rather easy, no credit card required, you just have to bellydance your internt braowser to death.

Thanks for your questions, and i greatly look forward to your release of new questions, feel free to ask! ;)