CPU and Memory

You buy a new computer. It says it has a Pentium M processor with 2.13 GHz. What does that mean.
Also the computer would contain DDR2 SDRAM with 256 MB and 400MHz. Again, what does that mean.
What happens if you have a "slow" processor?
What happens if you have a small memory?
Can you compensate a small memory with a large (say 100 GB) hard disk?
What are the two main differences between primary storage (memory) and secondary storage?