There's some reasonable introductory stuff on here:
http://developer.valvesoftware.com/wiki/Category:XSI
I know its Source related but the modelling process is pretty much the same, only really starts to get different around the export stage (or possibly the animation stage, it's been a while since i've faffed around with Source modelling)
I particularly recommend Desty's Colt 1911 Video Tutorial, it's linked to on the above page but heres a direct link anyway:
http://halflife2.filefront.com/developer/Desty;10390
It provides a very thorough demonstration of the modelling process, though finding Tutorials on the following UV phase is a little harder. The XSI texturing page (
http://developer.valvesoftware.com/wiki/XSI_Texturing) contains a brief overview of the process, there used to be a small collection of .pdf files covering the various stages with a rather in-depth tutorial on UV mapping specifically, but it appears to have fallen off the internet
.
Other than that, theres the softimage wiki (
http://softimage.wiki.softimage.com/index.php/Main_Page), though I don't recall ever using it so I'm not sure how useful it is. Theres also a large amount of them on
http://www.edharriss.com/tutorials/tutorials_all.html but again, I've never used them so they may not be that helpful, they always seemed more inclined towards modelling for art's sake rather than making something functional and (comparitively) low-poly for use in a game.
Also, I recommend installing the RO SDK and using it's animation browser to examine Tripwire's meshes up close and in detail, as a lot can be learned from seeing how the stuff that's already in-game was put together.
It's a rather sparse collection, it seems like the documentation for it has been scaled back since the days when mod tool 4.2 was publicised with HL2. Still, the above tutorials have some handy information in there, so I hope the links may prove helpful.