Started over from scratch on that embark, and... seasonal save didn't seem to take. Only save folder left is... sigh; the embark. May just reinstall if this happens again.
I'd go back to the old DF, but... so many minerals. So many layers. Bauxite everywhere!
My recommendation would be to delete all traces of the old DF you can find, and install from scratch into a folder that is not in any way related to Program Files or any other "special" folder, like your Desktop. Under Windows 7, the evolving standard seems to be c:\users\public\games\ and it's not a bad choice for Vista either.
Once it's installed, make sure that your user ID has "Full" rights, or at least read / write / traverse / execute , to the entire chain of folders, and to all files in the df folder and its subfolders.
Regarding freezing PC, I've had DF 2010 fail, but never take the whole PC with it. DF 2010 can take up to the 32-bit Windows limit for a single program of 2 GB, and occasionally wants even more (site finder on large embarks, etc.), which causes DF to fail with a Windows error. If you have less than a bit over 2 GB of memory available for DF (after OS, any other programs you're running, etc.), that could potentially cause more serious Windows problems. If you don't have that much physical RAM, make sure you have enough virtual memory allocated (a minimum of 3 GB, and preferably more), which will be slower but better than crashing.
The other possibility is that DF can stress some computers more than other software; if you don't have adequate cooling or power supply this can cause shutdowns or lockups.