A customer reported this last Friday. After he installed Softimage 2011 SP1, he uninstalled 2011, and after that Python did not show up as a scripting language in 2011 SP1.
I uninstalled 2011 and sure enough Python was gone in 2011 SP1.
To get Python back, open a Softimage 2011 SP1 command prompt and run runonce.bat.
Note that on Windows 7 or Vista, you’ll have to use an elevated command prompt (right-click the Command Prompt shortcut and click Run as Administrator).
eX-SI 
can you clarify: Does this happen if you uninstall 2011 before installing SP1?
The problem happens only if you uninstall 2011 after you install 2011 SP1.
Could you tell a noob how you go about doing the fix?
I am not sure how to go about opening a command prompt to softimage etc..
On Vista and Windows 7:
Awesome thanks so much! I was going the very wrong way about doing it.
Thanks again š