You can get different light colours in the same scene......daylight coming through a window will be a different colour to the lamp that's on in the corner of the room.....
I think (and I am by NO means an expert, so am probably wrong) that using a grey card will only give you the 'correct' white balance for the light falling on the card. For example, if the white card is placed with daylight from a window shining on it, but there is a lamp in the corner of the room that doesn't reach that far, then it won't have much/any influence on the white balance result, so will probably look very orange in the 'corrected' image.
My SB-700 came with an orange & a green clip on filter to correct it to incandescent & fluorescent lighting. Newer bodies will even detect this filter has been fitted & adjust the white balance accordingly. On my D80 this has to be done manually.
At the end of the day, white balance is largely subjective. You might take a pic of a room that looks quite cold/blue and comparing it to the actual room it might be spot-on accurate.
But, you might actually want a nice warming appeal to the room, so you would perhaps shift the white balance to give it a bit of a warmer glow.....or exaggerate the clinical nature of a laboratory or hospital by making it colder and more stark.
Regarding HDR & Elements - I don't think Elements specifically has an HDR function.
I recently looked at the latest Paintshop Pro though, which does and is pretty cheap for a fairly comprehensive package.
Ideally I want to get CS5 and am currently looking at doing a local college evening photo course, so I can get it at educational cost...