i dont use xsi but i did a bit of a google and came up with these sites
http://www.highend3d.com/xsi/tutorials/
http://www.xsifiles.com/
http://www.edharriss.com/tutorial.html
http://www.tutorialguide.net/3d_software/softimage_and_xsi/
i hope they are useful to you.
Krypbob };-))
http://www.alias.com/glb/eng/products-services/product_details.jsp?productId=2300004
The Personal Learning Edition is free to download
also www.3dbuzz.com has some really good softimage beginner tutorials