Sorry buddy, but i'm in the exact same situation and theres no solution.
Windows just plain doesn't have the drivers to read Apple Software Raid drives. Apparently there is work in the linux world to get it working but thats about the extent of it.
This is why Apple should enable the hardware raid that is embedded in the MacPro chipset!
Also, BEWARE OF OS AND FIRMWARE UPDATES!!! Apple does not support booting from software raid AT ALL, even though it allows you too. When I updated from 10.4.7 on my MP it caused a kernel panic during boot up. I and others found the only way was to install the update onto the disk while booted from another drive. Same goes for firmware updates, it must be run from another non software raid drive or an external firewire or usb drive.
Anywho, the speed boost is still pretty nice and besides apple not supporting the hardware raid in the MP, I'm still a happy camper.