How much RAM is inside the iPod?

32MB DRAM + 96 or 128kB SRAM (aka IRAM, fast RAM). The 60GB iPod video has 64MB DRAM.

How fast is the iPod?

Speed depends on more than the clock speed. The iPod Linux kernel clocks the CPU and COP (they cannot be clocked at different speeds) at 75Mhz on all generations.