Writing a book is an interesting mix of experiences. I'd recommend trying it once for anyone that has an interest, but doing more than one requires a certain amount of crazy (this will be #5 if that tells you anything).
So the normal process (with Syngress anyway) is that you get a bright idea, and then fill out a proposal form (http://tinyurl.com/syngress-proposal
) and send that in to the acquisitions editor. They take a look and, if they are interested, send the proposal through the approval process. This consists of a review by a few folks who are active in whatever the topic area is (they may or may not ask for revisions at this point) and a couple passes through internal review meetings where they decide whether the proposal is viable or not, i.e. will anyone buy it, are there 17 other books on the exact topic, etc.. This usually takes at least several weeks, but could be quite a bit more.
Once your proposal is approved, you get a contract. The contract will say how long the book should be (in number of words, for which there is a magic formula to figure this out), when exactly it needs to be done, what royalties will be paid, etc... all in nice legalese. If you are working with another author, the contract will also say who gets what % of royalties and who gets what advance on them. More authors = more slices of the pie. This can take another several weeks or more to get worked out.
Once all this is sorted out, you get to work writing. I generally jump the gun a bit and get going as soon as I know that the proposal has been approved, but that's just the way I'm wired up. Usually, you will have a developmental editor (DE) assigned at this point, who will work with you to figure out a schedule to turn in chapters (something along the lines of the time between now and the due date, divided by the number of chapters), and who will also take the first editing pass at your content for spelling, grammar, etc... The DE is sort of like the PM for your book and will generally be someone working for . You will also have a technical editor (TE) who will be someone outside of Syngress and theoretically someone who knows the topic who will be looking at your work for technical accuracy. Lastly, you may have a copy editor who will do the final polishing of your work after all the editing is done.
Usually, the process goes something along the lines of: you finish a chapter and send it to your DE who marks up a few comments, they send it to the TE who marks up a few more comments, then send it back to the DE, the DE sends it back to you, you fix what needs to be fixed and send it back to the DE, the DE sends it to the copy editor, the copy editor sends it back to the DE, and then it's ready for production (whew). The writing process is usually somewhere around 6 months.
Once all of your chapters are done, your book goes off to be typeset and finalized. Somewhere in here will will get to see the cover of the book as well, but you usually have to ask for it. You will generally get a chance to look over the final proofs to make sure that nothing strange has crept in, then the book goes off for printing. This takes about three months (so we're creeping up on a year here altogether).
As you may have picked up, this is an enormous amount of work and takes huge amounts of time. If you can get multiple authors together to do a book, this obviously lessens the load, but it also lessens the monetary rewards. You should absolutely not expect to crank out one book and expect to see any significant amount of money back from it at all. If you have several out at a time, it does add up, but it is still fairly small, even when compared to flipping burgers.
On the other hand, you do get a certain amount of credit and recognition for writing a book. It's very cool to have a complete stranger come up to you and tell you how great your book was. You can also sink a huge amount of time into watching sales figures and sulking over shitty reviews that have no basis.
Whew. That's enough for now, but I'd be happy to answer any additional questions.