Access to \device\physicalmemory

of course, using same tool you can setup one IDT-entry (instead of GDT),
& go to Ring0. in XP from 42h to FFh INTs are reserved, so enjoy with them.

huh, why you need CR0 for write in IDT?? nop

[edit]:
forgot, when you will in Ring0, perform same action, wich does other system INTs..
save in same order registers, load then in FS-reg 30h..then only can be STI..
(stack should lowered on 68h or more from entered position)