In case of any problems with booting GEOS under emulator:
- setup emulator for 1 x 1541 and a REU
- boot GEOS
- change drive configuration in emulator prefs
- execute CONFIGURE from bootdisk, setup your system and save the configuration

From now on you can boot system with desired drives selected before boot.

update:
- you may boot GEOS faster by executing only 'GEOS KERNAL' file