Software Suspend, or swsusp, is a method for suspending to disk based purely on software, that is, not requiring APM and ACPI. Pages are swapped to disk along with some control information, and read back the next time Linux boots. It works for pre-APM hardware and for those whose APM/ACPI implementations are buggy (such as certain laptops).
Since it's based on software and only kicks in at some point in the kernel boot processes, nothing keeps you from loading another OS instead. Just make sure that the other OS does not modify mounted partitions, since Linux will expect them to be exactly the same when it unsuspends.