I started a thread on discussions of integrating bitcoins into an MMORPG environment on this thread:https://www.bitcoin.org/smf/index.php?topic=353.0
I know that doesn't quite answer your question, but the issue of integrating bitcoins with specific games is something useful. Perhaps the independent API interface (with a DLL or library file of some sort) could be developed to also facilitate the development of such clients.
As for specific games, the main interaction would be through some kind of virtual money to bitcoin exchange. I would discourage such an exchange for games that don't want "real world money" involved (Runescape, World of Warcraft, etc.) but there are many games that don't mind having "real world money" attached to their virtual currency (Second Life, to give another example).
If you want to set up an exchange between this particular game, Progress Quest, and bitcoins..... have fun! I hope you succeed and get something accomplished. If you are looking for some technical responses to how that can be accomplished, what sort of problems are you facing in terms of making that implementation?