Your PSU is enough to run the 9500GT.
Your motherboard supports a limited number of Phenomx4 processor chips. Honestly, none of those are good enough for gaming on max settings. You're looking at a Phenom x4 which is at least 3GHz. Sadly, the ones supported top out at 2.1GHz. Here's the list of those supported:
http://in.asus.com/Motherboards/AMD_AM2/M2NMX_SE_Plus/#CPUS
You would not be able to play Black Ops and/ or Witcher2 on 'highest settings'. You may manage them on low settings though.
Suggestions:
You may want to consider a new motherboard if you're looking at getting a good Phenom x4 chip, and if you're looking at maxing them games out. If that is an option, let us know.
Upgrading to a 9500GT is not recommended as it is a very weak card for games of today's standards, as also Black Ops and Witcher 2. You're getting a good CPU, but it would be bottlenecked if you got a 9500GT.
A lot of options are available as regards GPU's today. Tell us your budget, if you're interested, and we can give you recommendations on GPU's. Depending on your choice of GPU, we would next recommend a PSU. It would most probably be 600W or more.
See if you're in a position to upgrade the rig as said above, you can get a decent gaming rig depending on your budget.