Hm this sounds like you have the old demo version. Your specs should be fine. Did you try out any other Direct X8.1 based game? Just to make sure it's not the video drivers.
Does it crash during the game only or also in menu mode?
I was not able to reproduce any crash on a new, old and on a very old system, under Win XP as well as Win 98.
In the new demo the empty pointer issue is fixed. The new demo displays "Ver.11d" during the splash screens. If this is not the case, you still have the old demo.
If this still is not the case after downloading the demo again, it might be possible that your ISP still has the old file in the proxy. I've had that before.
If I have some more webspace available I'll upload the emo again under another link, to make sure it really is the new one, but for now I'm afraid I have to leave it as is because of the contest (This means one more week).