There's not a whole lot you have to do to convert to using EPGP instead of DKP, largely because the fundamental difference between EPGP and DKP is that EPGP divides the earned by the spent where DKP subtracts the earned from the spent.
To make the system do this calculation for you, simply edit the "DKP System" and check the box labeled "This is an EPGP System." Once that's done (and you've run the GetGRSSDKP.exe program accordingly), the everything else is done in exactly the same way: Recoring how many points were spent on items (GP), and how many points people receive for attendance (EP).
Sounds easy enough, I'm going to assume that GRSS doesn't know the value of each item(GP) and that will have to be entered manually, correct? Also should I be able to award EP through GRSS or through the website or both? Another question, How to set up the Decay since with EPGP Decay is a % after each raid and does it decay both EP and GP?
*EDIT*
I just got the email about the big over haul on the GRSS and the forums as well. I'll just wait to see how things pan out. Until then I will continue to use the GRSS specific to loot tracking for the website and use the EPGP mod for the tracking of points.