Hi Chinna,
Yes you can go for PS training and work on SAP PS.. but logically it would make more sense to go for FICO.. what happens usually is that once you gain experience in one module of SAP you tend to learn other modules as well during the journey..
So if you learn FICO you will come across SAP PS integration points.. and can learn PS as well.. similarly you can learn PS and get to know FICO and other areas..
It all depends on in which are you are comfortable with.. are you happy handling projects and project management activities or you are a Accounting person... If its the former you go for PS and if it is later one go for FICO.. 
Hope it makes some sense to you...
Regards
Sammar