One entity can have only one form.
The work around is to show/hide fields/tabs using JScript for different Users/Roles.
You will have to wait for CRM 2011.
But there is a company http://www.c360.com that has a commercial add-in that will do it.
Hi Liron,
CRM 4 only supports one form per entity. Via javascript you could hide/show fields and tabs, but there is no mechanism to actually create a new form for the same entity.