Yes you can. Will you benefit from going faster? Not sure. That depends on how upgrade-able the 6000 is in terms of the CPU and if the laptop allows for a CPU with a faster corresponding FSB that can take advantage of the faster RAM.
Latency: This is the delay between when an operation is requested and when it is performed. The shorter the delay, the less of a performance hit you take. Traditional DDR is easily made to go as low as CAS2, and usually can be had for a good price and found with ease. With DDR2, you have latencies that are typically CAS4-5, but we're starting to see them work toward traditional DDR CAS timings.
Okay, why switch to DDR2? The design of DDR limits how high it can eventually go. DDR2 is supposed to raise that ceiling.
