hey folks? which is the best ram to get? i need a new fast PC and i am looking for fast RAM ... and i would buy the rest of the pc fitting to the ram

This may sound a little harsh, but that is completely the wrong way to go about building a PC. Someone has obviously mentioned to you that memory bandwidth is a serious contributor to performance, which is true. However, memory should be purchased to fit system architecture at maximum specifications. There's no point going out and buying DDR2 800 (12 GB/s, if you can believe it) because to effectively use it, you'd need a Pentium 4 Extreme Edition 3.46 GHz or 3.73 GHz, which are completely ridiculous processors.

Components should be picked in the order of Processor, [Graphics Card,] Motherboard then Memory. The type of RAM you get depends entirely on these two things.

When it comes down to it, as long as your memory meets the maximum specifcations of your chipset/processor, the fine details such as manufacturer and latencies account for next to nothing in terms of performance. These details become important only if you plan to run components out of specification. i.e. Overclock them. If this is the case, choose a decent overclocking processor like an Athlon 64 3200 and up and a DFI motherboard, then start thinking about RAM.