I went to a mac forum (I already belong to two) and posted the question. So far no answers. I thought this might be an issue others have seen before, perhaps with Leopard, but apparently not, or not by these users. So I made an appointment at my local apple store and will bring my computer in. This seems the best solution, if they will help me. I am not sure what the limits are on what help they will give me if I am not a member of their "procare" program - I have applecare, which gives me help by phone but for whatever reason it does not extend to help in the store. I really don't want to purchase another tech help program. Seems like overkill.
So I am feeling sad. I realize I mainly have to work through some things. There may be some basic things I am not doing regularly, although I doubt that, some sort of regular maintenance. I think it more likely that this is a Leopard issue. Leopard hasn't been out all that long and some things are bound to come up. I do feel good that I can at least bring my laptop to the store! Lucky!
Yesterday I brought the laptop into the Apple store. Of course when we started it up it worked perfectly. The tech did some diagnostices, found some permissions errors and no hard drive problems, and we called it good. So I still don't know why it froze and neither does he but I'm hoping it had something to do with the permissions and never does it again. At least not for a long time.