The latest 8051/52 development system is updated on WEB.
Please download http://www.bipom.com/devsys/8051dev.zip and install it to your PC.
The newest release contains the improved help and a lot of new examples.
Run Micro-IDE and click Help->Micro-IDE Help (8051 Development system).
"Customizing Toolkits" chapter explains how to add a new toolkit in details.