If you purchased them WITH the system, then they are "OEM" versions, which you would have purchased at a discount with the computer.  OEM licenses are NOT transferrable, so, yes, you will need to purchase them again.  For future purchases, if you purchase them separate from the PC, then they ARE transferrable.  It will cost a bit more, but they will be more flexible.
I need to replace my Dell, what do I do about my microsoft student package and mcaffee which are already installed on my current dell? Do I have to purchase them again? Thanks
Need to replace my Dell