1)For Windows
Go to http://python.org/download/    and download software depending on your OS’s architecture
2)Linux
a) First Search in your Package Manager for python 3.0 (it probably is installed) if not try to install from the repos else:
Go to http://python.org/download/ and download the bz package and extract it.
b) Open a terminal in root / superuser mode
cd <dir>
where <dir> is the path .
c) ./configure
d) make
e) make altinstall (this preserves current python version , else do make install)
If you get any dependency errors ,don’t be scared just try to find them using your package   manager or use google to find them.
For Old Python Users:
– Basic syntax had changed but you would get used to it.
– There’s a tool to convert old syntax scripts to new 2to3 .(unstable)

Windows users can add python to their environment variables
My Computer>Properties>(Advanced System Settings in vista)>Advanced
Go to Environment Variables >Scroll bottom scroll bar, select PATH and click edit
Add to the end ;<path where its installed>;
Now a script can be written anywhere and executed by

python <file-name> in dos
-Open DOS or terminal and enter python or python3.0 .Upon pressing enter an interactive shell
shall open with current python version and install date and time and OS type you are using.