You may want to run drwtsn32 and change the dump type to full, but I can tell you from your minidumps that the reboot isn't really a reboot - it's a bugcheck (BSOD) STOP EA, and it looks like the culprit is the file ati2mtag.sys, AKA your video driver.
All three dumps have different functions that are causing your crashes, but all have hal.dll in their callstack, which may mean that the problem that caused a GRAPHICS_DRIVER_FAULT may be hardware issues as well - just an FYI, if the driver update (or, downgrade, if you're using the latest) doesn't solve it.
This post has been edited by cluberti: 02 January 2006 - 08:26 AM