Based on my experience and questions i answered on magento community board i decided to compose Magento Developer Cheat Sheet - a bunch of commands you as a magento develop would find useful.
If you're using magento 1.3x and php 5.4 and encouter this error:
Can't retrieve entity config: core/store_group
then simply replace lib/Varien/SimpleXML folder of magento 1.3x with the same folder from magento 1.6x-1.7x.
The error happens due to outdate SimpleXML library that is not compatible with php 5.4.