wompedy,
Since Parallels Desktop 4 the VM's hardware is fully ACPI-compatible. If after some period of inactivity Windows decides to go to sleep mode - the VM will be paused. Thus, the behavior is controlled by your Windows' power scheme. The idea behind this is power saving - if you're on battery, the VM will pause soon thus saving battery power.
You can control these periods in Start->Settings->Control Panel->Power Options. If you don't want windows to pause anymore, just set "System Standby" to "Never"
Last edited: Nov 26, 2008