SD (Standard Defintion) captured from a tape camera via Firewire is the easiest to edit... AVCHD and DSLR require a LOT more computer power
Look for 2 hard drives, or SSD and 1 hard drive, and a CPU appropriate to the kind of video you will edit
These links are more aimed at Premiere Pro... but you still need a laptop that is going to be strong enough for the kind of video you will edit
Laptop Video Editing PC
If at all possible, do NOT buy a laptop with "dual video" since that is very likely going to cause problems
Dual video laptop problems
-link to why http://forums.adobe.com/message/4685328
-HP Fingerprint/Password conflict http://forums.adobe.com/thread/911575
In general, for a given performance level, a Mac will both cost more AND be harder to upgrade if needed (adding ram or a 2nd hard drive)
This message has a really good graphic about requirements - http://forums.adobe.com/thread/810750
I agree with John T's comments.
For SD Video editing, a Quad-core CPU should be fine, and I doubt that you could find a new one, with a Core-Duo CPU.
For any AVCHD, or HD Video editing with the H.264 CODEC, I recommend an i7 CPU, and the faster, the better.
If you are going to install a 64-bit OS (most likely), then you are correct to look for at least 8GB RAM minimum, as 4GB is just about enough to run the OS, with little left over for programs, and especially programs like PrE.
The two physical drive (whether SSD, or HDD) suggestion will be a big benefit, with Video editing. I feel that a 3x physical drive system is even better, but there are very few laptops, that allow for even 2x physical drives, and fewer still, that allow for 3x physical drives.
Be sure to read John T's links on the video card/chip. The most important aspect is the video driver support, as PrE, and now PSE, rely very heavily on updated video drivers. AMD/ATI and nVidia do a very good job of updating their drivers. Intel... well not so good, and many have had issues with dual-video cards/chips, but those configurations are very popular with lower-end laptops, to save on battery life. They work well with a lot of general programs, but not so well with programs, like PrE, or PSE.
PS - I am a big fan of the Sager, and the ADK laptops for Video editing, but they ARE pricey. However, they can be custom-built to do a great job with Video editing.