G'day Darb,
There's probably swags of different ways, I found this simple procedure on another site and use it heaps, only takes a few seconds using two different exposures, or even the same pic with different EV settings when converting from NEF:
1) open both the low exposure and high exposure images,
2) make the low exposure image current
3) ^A (to select all) then ^C (to copy to buffer)
4) make high exposure image current
5) ^V to paste the low exposure image into the high exposure image
6) Go to layers, make sure the pasted low exposure layer is current
then make a mask but clicking the icon that looks like a camera from
the front (didn't know how else to explain it...)
7) Alt-click on the mask window (the white window in the pasted layer
pallette) This should give you a white screen/image
Then paste into the white screen, this should give you a black and
white image
9) Then just click on the background layer to make it current and hey
presto! Merged exposures...
10) Then you can make the mask layer current and hide the background
and clean up erasing the bits of the mask you don't want...
Cheers mate.