You forgot to mention the most important issue, the codec used. For HDV your system is marginally OK, it will do the job eventually, but at a snail's pace. If you are talking about AVCHD, the system is way underpowered. It may appear like a retired snail that brakes before cornering.
Laptops are almost never a good idea for editing, they lack the muscle in terms of CPU, RAM and disk I/O and are around 10 times slower than an equally priced desktop. People using laptops for editing are either always pressed for time, so they must edit on their commuter flight at a snail's pace, or have very masochistic inclinations to suffer that performance level.
Consider the codec as the engine in a car, the under-the-hood stuff that makes it possible to get from A to B.
The distinguishing factor is the energy source, it may be gasoline, diesel, hybrid or some esoteric fuel, like methanol or even LPG. To continue in this analogy, CS4 has no problem with gasoline (DV type2) and diesel (HDV, XDCAM, P2), or hybrid (AVCHD) but trips over methanol or LPG (DivX, Xvid, and the like).
The LPG types are for watching, not editing. City busses running on LPG can be used to transport you from A to B, but you can't drive it yourself nor can you determine your own route (no editing).
Hybrid (AVCHD) may be the way of the future, but they are not the quickest way of transport, comparable to the strain on your computer.
Diesel (HDV, XDCAM, P2) is used for long hauls with attractive fuel consumption, making it economical. The start-up time and the noise (the burden on the system) are the downsides.
Gasoline (DV) is still the most versatile. Most cars have a gasoline engine, it is fast, widespread and easy to maintain.
Maybe this analogy will give you an idea what codec means. A useful utility to determine what codec is used in your material is G-Spot or MediaInfo.