How to run python in different directory?

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http://stackoverflow.com – I am doing maintenance for a python code. Python is installed in /usr/bin, the code installed in /aaa, a python 2.5 installed under /aaa/python2.5. Each time I run Python, it use /usr/bin one. How to make it run /aaa/python2.5? Also when I run Python -v; import bbb; bbb.__file__; it will automatically show it use bbb module under /usr/ccc/(don't know why), instead of use bbb module under /aaa/python2.5/lib How to let it run python2.5 and use `/aaa/python2.5/lib' module? The reason I asking this is if we maintain a code, but other people is still using it, we need to install the code under a (HowTos)