I recently got my sister's old laptop over the Christmas break.
OS is Microsoft XP Professional.
It was working fine at home (Internet, music, videos, etc.)
But yesterday I found a problem.
When I turn on the Wireless Internet switch, I get the BSOD with the message "IRQL_NOT_LESS_OR_EQUAL"
Laptop then restarts & will continue to restart until you switch the Wireless Internet switch to off.
Note: Laptop works fine when the Internet switch is off.
As the PC was working fine 2 days ago & I installed no new software, I have no idea how this happened.
The only thing I can thing of is the travelling...maybe some problem with the X-ray machine in Airport or something (?)
Try removing (uninstalling) the Wireless network driver and re-installing a new copy.
If the Laptop has been through an Airport X-Ray machine, I'd also recomend running a full disk check (including a bad-block test).