This can be accomplished well on R2008 and please see the steps below -
1. New an assembly and place the desired component
2. Save the assembly
3. Copy the assembly and its reference files to ...\Autodesk\Inventor 2008\Templates folder
When you create assmebly, you will get the customized template.
Thanks,
River
Thanks,
River Cai
Inventor Quality Assurance Team
Autodesk, Inc.
Email: River-Yijiang.Cai@autodesk.com