Serious Error Caused Unexpected Reboot

I’ve got a user whose machine reboots on occasion for no particular reason. She might be in Excel 2003 or just at the desktop. The error code after reboot is:

BCCODE 1000007E BCP1: C0000005 BCP2: 804EF73F BCP3: B2E33C44 BCP4: B2E33940 OSVer: 5_1_2600 SP: 2_0 Product: 256_1

The machine is a Gateway M685E puchased in May of 2007.

Any insight into what may be causing the computer to reboot and give this error would be greatly appreciated. Thanks,
TL