I don't know a lot about wordpress but I guess it has a table for users too ... The main problem is that it maybe won't call the same things >.> A bit below there's a topic about sharing user table on 2 boards of IP ( a tuto is going on ) but for Wordpress, the main problem is that both user tables are different ... But, basically, the meanings ( the way to do it ) stills the same.
I'm going to bed but if someone know a bit Wordpress and his SQL configuration I think he will be able to give you the answer