Thanks, that was a good hint! I found this thread, which was very helpful. Now I got Ghost Squad running but there were two other obstacles: vsg.xbe has to be renamed to default.xbe (actually this results in the "Please insert an XBOX disc" error) and tex_common.bin has to be removed (otherwise Xemu will get stuck at the AM2 logo) before creating the .xiso with the tool of your choice (I used C-Xbox). Apparently patching the XBE file is not required.
However, the game does not yet run smoothly as the FPS drop from time to time. I tried different BIOS versions and XBE patch on/off with latest Xemu.
