There are several companies that are making video tutorials for XSI, but not a whole lot of books. The XSI manuals really cover most of what’s needed for reference, and the video tutrials far surpass anything you can get in a book.
Unlike Lightwave, which requires a ton of 3rd party plugins to be functional, XSI does 99% of what you need right out of the box. There are a good amout of free plugins that cover most of the shortcomings. On top of that, Scripting in XSI is great, even if you are not a programmer and supports a variety of STANDARD scripting languages, so it’s pretty easy to find reference material for help.
i found XSI to be everything lightwave wasn’t and had completely switched over in about a month or two and have never looked back.
You should really download the trial version and give it a shot. The one thing you need to remeber is that this is NOT Lightwave. Much of what people do in lightwave is based aroung lightwave’s shortcomings (no edges tools, etc.) so it will seem odd that some things that were required to model anything in lightewave are not a standard part of XSI (spinquads for example) because they really aren’t needed.
As far as animation goes, XSI is years ahead and it will really blow your mind, once you realize allthe things you can easily do that were not possible without a ton of workarounds in LW.
Again, I recomend downloading the demo version and going through the tutorials. If you hit a problem, don’t freak out, come back here and ask about any problems. There are a lot of ex lightwave users here and most of the problems you may run into have already been sorted out here. =)
BTW, there is a spinquad type of script floating around, if you absolutely can’t live without it.