1) n900 must be upgraded to latest pr to support psx4m\pcsx
2) opex x-terminal -> root -> apt-get update -> apt-get upgrade
or open fapman\ham and use standard upgrade,should work fine
3) apt-get install psx4m-gui (dpkg -i psx4m-gui.deb) will answer question (guess only others psx emulator)
4) use apt-get and it will download all needed