I installed the first expansion first, Mask of the Betrayer. I launched NWN2. It crashed before it ever started. I tried to update, in case there were updates specific to MotB, but it said I had to launch the game before I could update; but launching the game hangs instantly.
So I uninstalled, thinking the issue was that NWN2 was fully updated before I installed MotB, which is built against v1.10. I reinstalled NWN2, didn't update it, just launched it, closed it, and installed MotB. And it crashed as soon as it opened.
So I installed Storm of Zehir. And it installed successfully. And NWN2 launched without crashing. SoZ is built against v1.20, so it was a short trip to the current latest v1.23, which also launches without crashing. All is well now.
Just thought I'd post this for anyone having Neverwinter Nights 2 crash on Windows 7 after installing Mask of the Betrayer. Try installing Storm of Zehir (if you've got it) and see if that helps. I don't know if you have to install against a base (non-updated) copy of NWN2, as I haven't tried it with updating NWN2 fully then installing the expansions. However, given that there are no catch-up patches and you have to install all the intermediate patches to get the boxed v1.00 up to the current v1.23, installing MotB and SoZ may be the fastest way to get a fresh install fully-updated anyway.
Hope that helps somebody out there!