Is it possible to use my digital camera sd memory card to transfer pictures back to the memory card from pc?

yes it is, just copy paste in you memory drive [SD] from comp.

yes - the SD memory card is no different than a USB memory key - as long as your computer has either a slot to plug in an SD card or you have an external device to plug in the SD card.
In Win XP you might see it come up and tell you that there is a new hdd in your system, noted as a 'removable drive'. You can then transfer pics to or from the card on your computer. hope this helps

yes you can, I do it all the time. The only thing you'd have to pay attention to is whether or not you camera uses any type of special file type association while saving your pics. What you could do is plug the memory card into your PC and open up the folder that you camera save the pictures in. Once in that folder, you can then transfer pics from the card onto your PC and vice versa.