|"does it mean that the effective speed of my new RAM i.e, ddr1 of 400mhz is going to be 800mhz due to ddr technology?"|
NO! DDR400 runs at 200MHz frequency. But because of DDR technology, the speed is "effectively" doubled. If you want to call it 400MHz, that's fine, but you need to understand that the actual frequency is 200MHz.
In the following chart, frequency is called bus speed, hopefully it will help your understanding of the different types of DDR-SDRAM:
"Does it mean that I should get ddr1 RAM of 200mhz frequency"
You already have DDR1 RAM that runs at 200MHz frequency.
"Is pc3200 ddr400 RAM a ddr1 ram or ddr2 ram?"
The number 1 generally isn't used for the 1st generation of DDR-SDRAM, therefore DDR400 is DDR1. If it was DDR2, it would be called DDR2-400.
Going back to my 1st response: We need to know the make/model of your motherboard.