Windows – or “my hardware is NOT real!” In DOS (Disk Operating System) the hardware was real and used a limited number of interrrpts to set flags that were readable and resettable directly by programs. In XP, and to varying degrees all the way back to ’95, Hardware is ‘virtualized’ and NOT directly accessible. This means that interrupts are recognized and processed by ‘Windows’ and messages passed up to the programs. The virtue of ‘Overlapped’ I/O is removal of timing requirements and enhanced system stability, the downside is ‘NO direct access’.
Decision time – If you want XP stability and multitasking then adjust to a ‘virtual hardware’ reality. If you have to have direct hardware interaction, then run DOS or some of the third party interfaces that gain direct control at the expense of multitasking and accept the crashes you will have. RTOS (Real Time Operating System) can do what you are attempting but it is NOT Windows and does not want to be.
The more you want ‘Windows’ with multi-tasking (e-mail AND Internet AND Word Processing) the less tolerant of ‘bit-twiddling the system can be.