I don't have your device, but you can check out this
link to get you going. Basically you need to be able to manually enter the bootloader mode. On iPAQs this is usually accomplished by pressing the Contacts+iTask+Reset button simultaneously for a few seconds and then the device goes into bootloader mode. You should then be able to try and run the flash program again. If this fails then you should try the link I provided which automates the manual installation of the rom upgrade. Also, don't even try upgrading your device under Vista. Lots of people have bricked their devices that way. Hope this helps.