some ideas:

1. electronic devices degrade in time and with usage.
2. different software means different usage of hardware, most notably different drivers.
3. as a conclusion: your 'stable' settings could be just on the edge of being mostly stable in XP but not being stable in 7.

don't page fault BSODs and other random ones point to faulty memory? run memtest from a cd.

but there is always the chance of unstable software, which is far more likely than my upper thoughts

gl