I would guess that there are a lot of poker scripts on the net, so it would probably only need to be an integration of a script.
I do like the idea of having some BBS-like extra fun, I ran a BBS too a long time ago. Don't know if I'd use a poker script, but some other small scripts would definitely be fun.
I don't quite get what you mean by the modified credits needing a different string for each person? Wouldn't it be possible to just add another field to w3t_Users called U_Credit or something, which would be used in the poker game and shown on the profile. It could even use one of the extras.
I've been thinking of adding a credit system which is based on more things than just the number of posts. Number of logins, having filled out the profile, voting in polls etc, would all give credits. It should also be possible to add extra points for people that have sponsored the site and stuff like that.
A lot of people were crazy about the credits on the bbs:es I visited (and my own) and the post count surely is important for a lot of people on my current board. So it would probably be a good way to increase activity, even though I don't really understand why the "credit hunt" is so important.