I don't know about the RPG stuff, but the registration and high scores bit is an absolute doddle.
As soon as you learn a little SQL getting the list of high scores would be as simple as running the query
SELECT score FROM playerscores ORDER BY score DESC LIMIT 10;
That would also limit it to the top 10.
Do a search on finding form variables with $GET and $POST, as soon as you understand that then try and set up a database and put values in and pull them out again. Might sound hard at first, but within 2 weeks you'll be laughing at how easy it all is.
