If you have a license for Parallel Computing Toolbox for R2008b or later, and you are not using a Student license, then you can probably use the link
Note: for this purpose I guessed that you are using 32 bit Windows.
If you are using a Student license then I am not sure if you will be able to access previous versions.
If you do not have a license for Parallel Computing Toolbox for R2008b or later then Parallel Computing Toolbox will not be offered to you for downloading on the link I posted.
It is no longer possible to purchase the toolbox for a version that old; if you do not have a PCT license at all then you would need to update your license to the current version and purchase PCT against that; after that you would be able to access the older versions.
