To get into board gaming, the best resource seems to be http://www.boardgamegeek.com
It might seem overwhelming at first, but there's so much information there.
Also don't forget to watch Wil Wheaton's Tabletop on Geek and Sundry: http://youtube.com/geekandsundry
RPGs I'm less familiar with.
On the Discworld front, the following board games already exist:
- Guards! Guards!
- Significant Quest (fan-made game played at Australian Conventions)
Coming soon is The Witches (also by Martin Wallace, the man who designed Ankh-Morpork). He also has grand plans for a third game too.
Of course you could probably play Cripple Mister Onion too with the rules from Turtle Recall.
RPGs: there were the Discworld GURPS and Discworld GURPS also released in the 1990s.