Nvidia 550 fx but doesnt support pixel shader 2 what to do

While it is possible to emulate pixel shader with software like "swiftshader" or "3d analyze" doing so only puts the workload on your CPU. Unless you have a hugely powerful system, emulating pixel shader will most likely result in unacceptably low performance and system instability.

More than likely, your best option is to simply replace your video card with one that natively supports pixel shader 2 or 3, they are not too expensive these days & will improve performance in other games as well.