Yep, PA-GE is supported only on 7200s with NPE 300 and later.
YOu can install PA-POS-OC3 module on a 7200 with NPE 200
Are you using a 7200 VXR ? For VXRs you need a min of 12.0(3) IOS, for supporting PA-POS-OC3 module. Your ram indicates you have a NPE 200 with 128 MB of RAM. .
Do you have 16MB FLASH ? Most of the 12.x images might need 16Mb flash.
Sankar Nair
UC Solutions Architect
Pacific Northwest | CDW
CCIE Collaboration #17135 Emeritus