I ran into something very strange today. I had a ThinkPad T41 that was getting intermittent blue screens of death. I ran hardware diagnostics, and they all came up with no problems. To make a long story short, I took it home and reformatted it. No more BSODs. Then I brought it back to my client's office, and I got a BSOD every time I booted up the computer - just after I logged in.
It seemed that whenever the wireless LAN card saw a WPA encrypted network (not even connecting to it - just seeing it), it would give this BSOD - about IRQ_less_or_equal (or something like that). I had to disable the WLAN card with the hardware switch (in this case Fn + F5). Then everything worked fine. In the end, I upgraded the driver for the Intel Pro 2100 3B driver (I think that was the model or something close to it). And after that, all was normal. Very strange.