Dream Station is a 32-bit DXI module, and cannot run in the x64 version of X2. It IS an included instrument - here is the Cakewalk link for the included synths:
http://cakewalk.com/products/SONAR/X2-Producer/ The Dream Station synth is not included by default in the installation, so unless you deliberately checked its inclusion in the install, it would not have gotten installed.
You can go back and install it - if you did not yet install a 32-bit version of X2 for your Windows 7 machine, just go back and install Sonar X2 again, but this time, pick the 32-bit version, AND make sure you select Dream Station this time - at the end of the install you will have a 32-bit X2 that will also have Dream Station installed.
If you DID already install the 32-bit X2 and just did not install Dream Station, just go back in and do another 32-bit X2 install, skipping the program files and just installing Dream Station - and any other 32-bit components, and you will be fine.
So, I hope that helps,
Bob Bone