Looks like the ISBN number is up on the Mongoose Publishing site now for the main rulebook anyway.
Mongoose_Matt released additional information on the enworld.org forums about the books.
Here's the bulk of his post, which was in response to his previous post which detailed all of the books to be made available this year:
Just a few notes to answer your questions and let you know what is going on. . .
1. First off, it looks like the first or second week of June for the main rulebook's release - a few printing issues have arisen. Still, cannot be helped and the book is going to look that much nicer because of it. Then again, with the Babylon Curse hanging over such projects, I think we have done damned well thus far!
2. Good news for hardback fans. The race books were indeed going to be 128 softbacks but so much material has been gathered and written for each that we are indeed going for 200+ page full colour hardbacks!
3. The price for the main rulebook (the biggest, fattest full colour you have yet seen!) will be $44.95. Supplements are going to be either $34.95 or $39.95 for the hardbacks and $24.95 for the softbacks. All, repeat all, will be full colour throughout, stuffed with photos, never before seen production pieces and original artwork detailing colonies, bases, starships and oodles else!
4. We don't personally handle preorders, as we want to fully support the retail chain. Start hassling your local games store to put a copy aside for you - we are going for an extended print run of this book but we have got some incredible feedback thus far. . .
5. There has been a fair bit of interest with regards to the B5 CSC - this is not an official Mongoose project so it will be handled completely by others. However, it is fully supported by us and will have its own section on the B5 sub-site when it goes online later this month.
6. Don't worry aboput an errata, Ranger - this book has been 'complete' for almost a year and has had the most vigourous playtesting of any of our projects!
7. Of course, yes, the Technomages will be covered - they have their own section in The Coming of Shadows supplement, to get them in your games, but will have their own book all to themselves. However, this will be a 2004 release.
8. Somebody asked about story arcs - these are the basic structure of a B5 campaign (though, yes, you can play B5 campaigns through more traditional means). Basically, a story arc is a connected set of scenarios combined with a healthy dollop of background material that allows GMs to create side scenarios where needed and give players things to do during downtime. Get 2-4 story arcs together and you have a complete ready made campaign. Combine that with the B5 story line (fully detailed in the main rulebook) and you have a setting and campaign like no other - kinda difficult to explain the concept in just a paragraph but there is an entire chapter dedicated to just this!
Hope that help,