Well, the first thing that comes to mind, is you want a desktop system, not a laptop.
That all being said, the answer is always the same with laptops: Get the best possible laptop you can afford. Get the fastest CPU with the largest number of cores, the most RAM, largest hard drive, biggest screen, etc.
Video editing will live and die by three main factors though.
1: CPU speed
3: Hard drive speed
Which is why you don't want a laptop. Mobile CPUs are not as powerful as their desktop counterparts, laptop RAM has fewer pins for reading/writing data, and hard drives are slower. So you're getting screwed in all three areas where it counts the most. But if you insist, see the above about getting the best possible laptop you can afford.
Also, make sure that you're using a codec that is multi-threaded, like x264, so that you can distribute the encoding load across multiple cores. Some encoders can even utilize the GPU for encoding video data, which is REALLY nice since GPUs are designed for stream processing, and that's EXACTLY what video encoding is.
I need some suggestion for buying a new laptop for video editing purpose. If infrared is included, that would be great.
The laptop I bought from last year is just too slow now.
I saw a lot of laptop offers with 2GHz, 3GB and 250-320GB hard drive with good price.
Is there a big speed difference between Intel Core 2 Duo with 2GHz and 2.16 or 2.4GHz? 0.16 or 0.4 doesn't look too big to me, but the price is a lot higher.
At this time I have one with:
Windows Vista Premium
Intel Core Duo - Centrino
160GB hard drive