eclipse installation
get eclipse
select a download mirror - i like virginia tech - this will download a compressed file to your computer
extract the archive - for windows, extract it to your program files directory - this will create a directory 'c:\program files\eclipse'
navigate to this installation directory and double click on the eclipse executable
get bpm
start up eclipse and at 'select a workspace' prompt say 'ok'
select 'help' from the menu, then select 'software updates'
click the '+' next to  'ganymede' - this will open a submenu of choices
select the 'available software' tab
click the '+' next to 'soa development' - again opening a submenu of choices
click the box next to the selection 'bpmn project feature' - then click the 'install' button and follow prompts
eclipse will install the bpmn add on and then encourage you to restart eclipse
upon restart, you should be able to create a bpm model inside eclipse (you will be prompted to setup workspace at each restart of the eclipse framework)
create a bpm diagram
under the 'file' menu, create a 'new->project'
expand 'general'
select 'project'
click 'next'
name your project and 'finish'
on eclipse splash page click the workbench icon 
your project should appear as a folder in the 'package explorer' tab
right click your folder and create a 'new->other->bpmn diagram'
double click your project, and then double click the file with the 'bpmn_diagram' extension
Eclipse is a development framework, it lives on your computer. You will need to create a workspace and then install the modelling toolset within that framework.

Here's how...
be sure you are in your extracted directory when you go to run the installation
download eclipse classic at http://www.eclipse.org/downloads/ 
you can download any eclipse version you want, but the classic version is...um...classic, and sufficient for bpm
note that eclipse classic is at the bottom of the list