Bilal,
'Rate the posts' meaning that if you think that the answers to your questions are right you might scores the answer. In the right corner at the bottom you will find a 'Rate the post' link or combo.
Regarding your questions, you can imagine a PG as a container of PIMs. A PIM manage a peripheral connection to an ACD or IVR.
For traditional ACDs or CallManager there are specific PGs available in Cisco Pricing Lists and they don't use GED125. These PGs use CTI connections to the ACDs and the CTI connection depends on the CTI link provided by the ACD (Avaya->MAPD, Nortel->Sympoium, CallManager->JTAPI).
Hope this helps,
Juan Luis