The 540m is more powerfull that the T9600 and produces less heat.
Intel Core i5-540M is a high end dual core CPU for laptops and clocks (due to the Turbo Mode) from 2.66 to 3.33 GHz. Each core is based on the Nehalem (Westemere) micro-architecture. Hyperthreading enables the Dual Core CPU to handle 4 threads at once (for a better usage of the pipeline).
The performance of the Core i5-540M is on average faster than a 2.8 GHz Core 2 Duo T9800 and in some benchmarks even faster than the fastest Core 2 Duo T9900 (e.g. 3DMark 06 CPU Score). Therefore, the Core i5-540M is a high end dual core cpu which should handle all daily work and gaming tasks. Only the quad core i7 CPUs can be noticeably faster at tasks that require four or more threads (e.g. rendering).