Parity checking is used to detect memory corruption between the time that data is written to memory and the time that it is read back. This error message means that there is a problem associated with the system memory.
There are many possible causes of memory parity errors, some of them only related indirectly to the memory, or even having nothing to do with the memory at all. I recently had 3 bad Vista installs in a row and it traced back to a corrupt OS disk from Microsoft so you are definitely right... it may not be the memory at all.
I can tell all you ppl that have the memory parity error (especially Dells) have a really hot running computer that's baking the gpu ram chips which in turn causes this error. If you are getting this, that means your gpu is pretty much gone and it will need a replacement. If your lappy is out of warranty, you're pretty much screwed.