Ok, I did a few tests, so here are the results:
0/ I attached the new nvidia-bug-report.log (after crash and reboot, but before starting X again)
1/ I seem to have the latest from HP (in any case, as this box runs exclusively under linux, I couldn't make an update)
2/ Up till now, I used the mandriva kernel 2.6.12-12. I updated to 2.6.12-15 (latest from mandriva)
3/ I tried it with noapic and acpi off.
The behavior remains exactly the same.