Adding new GFI circuit to existing sub panel.
 

Existing 100A sub panel is fed by three #4's in metal conduit. I presume the conduit is acting as the ground. I want to add two circuits that will need GFI protection:
1) Is the sub panel correctly grounded as is? -- (the existing feeds are hard piped also).
2) New circuits will be Romex and not in conduit. Do I need to add a grounding bar to the box for the GFI's or can their grounds share the neutral bar?

Might want to post a picture of the panel with the cover removed for better ansewers.

Neutrals and grounds cannot share the same bar in a subpanel.

Not sharing the same bar in a sub panel makes sense. Given that the box is grounded, when I add a second bar is it bonded (screwed) to the box like the neutral bar, or is it somehow isolated?