Mouse integration always starts enabled and the only way to disable it is via the GUI.
I run my VM on a completely separate X screen, so the host mouse and keyboard have no interaction with the guest or it's GUI (I use a USB remote to interact with the guest). This means that I can only control the VM via VBoxManage which mostly works fine, unfortunately if mouse integration is on, the guest mouse cursor is invisible and I have no way to turn integration off.
In previous versions it was possible under XP to uninstall the VBox mouse driver and roll back to the microsoft one, but with 1.50 this no longer works.
Many thanks in advance