Yeah, who is this member? Not to be rude, but if they don't want people telling you(if this is the case) who he is, then they're probably not to be trusted.
If you're getting a few thousand ($/pounds), then be sure to ask for an advance and make sure they're good for there money. Perhaps give them a few sample terrains or a compiled DBP .exe featuring the terrains to let them know you're good for your product
if they won't give you the advance.
Other than this advice, I hope the best for you, this is truly exciting news. If the publishing deal doesn't fall through, consider self-publishing. Somewhere down the road, you sparked someone's interest, so you must have a good product.
A book? I hate book. Book is stupid.
(Formerly Yellow)