Hi Lin,
With a registered copy of CCSv3.1, you should be able to use Update Advisor download CCStudio Scripting. This is done from Help->Update Advisor->Check for Updates from the CCS menu line.
If CCStudio Scripting does not show up in the Update Advisor list online, then it may believe that it is already installed. If that is the case, try uninstalling CCS Scripting and then try Update Advisor again.
For CCS version 3.1, Update Advisor is the way to download CCS Scripting.
You may also consider upgrading to CCSv4. CCSv4 uses a different scripting mechanism, Debug Server Scripting (DSS). If your development work in on a supported DSK or EVM, then there is no licensing fee for CCSv4. And there should be no problem having both CCSv3.1 and CCSv4 installed at the same time; if this is a concern, you may want to read up on the idea by searching the forum for any issues.
Regards,
Gautam