Did this in latest Poky 2.6 - Try to use poky > 2.1
bitbake core-image-minimal & bitbake core-image-sato
generates different set of images.

- check if you have enough disk space!
- check that you are not adding extra packages in your /build/conf/local.config
- check that you are using different local.config files while bitbaking core-image-minimal and core-image-sato. (If you have added packages while bitbaking sato then those packages will be added while bitbaking minimal, if you are using same local.config)
Just a suggestion, not that you have to do it:
If you are bitbaking for the first time use default /build/conf/local.config and /build/conf/bblayers.conf
(uncommenting DL_DIR, SSTATE_DIR, TMPDIR will be beneficial though)