Take a look at the Administrator's Guide > Project Customization > Generating Workflow Scripts > Customizing Defects Module Dialog Boxes

By default there are 4 pages/tabs available for the defect module. By default when you add a user defined field it will be added to the first tab. If you want to move fields to different tabs go to Tools > Customize... and select Workflow. It looks like there are two places to customize the tab displays - in the Add Defect display (Script Generator - Add Defect Field Customization) and in the Defect Details display (Script Generator - Defect Details Field Customization). And the customizations appear to be per user group.

I haven't worked with this area of customization before so can't provide much more information. You'll probably need to do some experimenting to get it exactly the way you want.