There are two reasons to use attachments. The first was touched on in the Point_Viewcontrol tutorial here, where you can set the PVC to always point at a particular feature on an NPC, Alyx's eyes in the tutorial.
Here is how to create your first character in SOFTIMAGE|XSI.
In this tutorial i will explain to the best of my knowledge how to use HLMV for viewing and editing models
A full listing of HL2 models by directory
This is not a tutorial of such, more of a reference and is only an introduction to the QC file.
Creating custom eyes in 3DSMAX for TF2
How to construct a prop in XSI, texture it, export it & compile to .mdl format and put in-game!
Guides you through creating your first Source mode in XSI.
A quick reference for source model compiling and decompiling. Includes links.
This is a short article describing the 2 options for moving around the viewports.
If you want to quickly compile a model by just right clicking on the QC and selecting an option to compile it, then you're in the right place!
You can't use Model Viewer to do it anymore. This covers rescaling prop models for Source.
How to add a custom sequence to an existing model
Modelling in Milkshape
Get everything set up for your first model!
Addicted to Morphine
Describes how to add extra skins to existing compiled models in the Source engine
Configuring XSI and using the SDK tools
I will guide you through the creation of a prop_physics entity, which may also be used as a prop_static entity.
Gmod Ragdolling with 3dmax
Rigging and animation for Source models, using XSI.
Training kit originally provided for free by Digital Tutors and Autodesk to train those learning Sodtimage XSI
How to work with TF2 facial morphs in 3DSMAX