I really don't know as I've never had any personal experience with the Physx cards, but I
can tell you that it is not a graphics accelerator, it is a physics processor.....it is used in addition to not instead of a graphics accelerator card. Here are some articles that you may want to peruse:
The Scientists' Opinions on Gaming Physics
Is Ageia's PhysX Failing?
Asus PhysX P1/128MB
PhysX: Six Months Later
Valve and Crytek won’t support PhysX any time soon
What you have posted in regards to your video, ATI Radeon Catalyst 1250, refers to the driver software (Catalyst) not the model of the card itself. When I look at
the Aspire M5100 Specifications, it has listed "ATI Radeon™ X1200 graphics solution". It does not say Integrated, like it does for Audio and Networking, so I don't know if it's integrated (chip built into the motherboard) or a separate expansion card. If it's a separate expansion card, is it removable from the PCI Express X16 slot? That is something that you are going to have to find out prior to purchasing a new video card, as you'll want to ensure that you have an empty PCI Express X16 slot to hold the new card.
I would look for a 512MB PCI-E (provided you have the available slot) card and also ensure that it supports Shader Model 3.0