I don't think its very usefull to use a PSX emulator to emulate the Sega...
Try to run a real PSX game. (2D like Metal slug X runs perfect

NYI:
It's very simple to create an ISO of your Disc, but I don't know how to do it on a Mac...
If you can do it on a windows machine (or virtual PC), I'd say get a program like .
Just make an ISO of your CD, and put it on your PDA.
If it's too big, you will need to .Z compress it.
Grab the PocketISO tool from the website.
I don't have GTA for the PSX, so I can't try to Rip it and make a guide for it

If the file still is too big, msg me and I'll see what I can do.
Oh and by the way, go grab , it's for the Mac too!
